Polyethylene with a high vinyl content and with a low MFR

ABSTRACT

The invention relates to a polyethylene having a melt flow rate at (2.16) kg loading (MFR2), determined according to method ISO1133-1:2011, which MFR2 is A g/10 min and A1≤A≤A2; wherein A1 is (0.5) and A2 is (1.70), and containing a total amount of vinyl groups which is B vinyl groups per (1000) carbon atoms, and B1≤B, wherein B1 is (0.45), determined according to method ASTM D6248-98, a polymer composition, an article being e.g. a cable, e.g. a power cable, and processes for producing a polyethylene, a polymer composition and an article, and an article; useful in different end applications, such as wire and cable (W&amp;C) applications.

FIELD OF INVENTION

The invention relates to a polyethylene, a polymer composition, anarticle, e.g. comprising layer(s), e.g. insulating layer(s), whichis/are obtained from the polyethylene or the polymer composition, thearticle may be a cable, e.g. a power cable, a process for producing anarticle which comprises use of a polymer composition, and processes forproducing a polyethylene and a polymer composition. The polyethylene,and polymer compositions comprising it, may be useful in different endapplications, such as wire and cable (W&C) applications, especially incable applications, such as power cable applications, e.g., in mediumvoltage (MV) and, for example, in high voltage (HV) and, for example,e.g., extra high voltage (EHV) cable applications. Further, thepolyethylene, and polymer compositions comprising it, may be useful inboth alternating current (AC) and direct current (DC) applications.

BACKGROUND ART

Polyethylenes produced in a high pressure (HP) process are widely usedin demanding polymer applications wherein the polymers must meet highmechanical and/or electrical requirements. For instance in W&Capplications, e.g. power cable applications, e.g., in LV, MV, in HV andEHV applications, the mechanical and the electrical properties ofpolyethylenes, and of polymer compositions comprising polyethylenes,have significant importance.

For instance in power cable applications, particularly in MV andespecially in HV, and EHV cable applications, the electrical propertiesof the polymer composition have a significant importance. Furthermore,the electrical properties, which are of importance, may differ indifferent cable applications, as is the case between AC and DC cableapplications.

Further, it is also known that crosslinking of polymers, e.g.polyethylenes, substantially contributes to an improved heat anddeformation resistance, mechanical strength, chemical resistance andabrasion resistance of a polymer. Therefore crosslinked polymers arewidely used in different end applications, such as in the mentioned wireand cable (W&C) applications.

Furthermore, in cable applications, an electric conductor is usuallycoated first with an inner semiconducting layer, followed by aninsulating layer and an outer semiconducting layer. To these layers,further layer(s) may be added, such as screen(s) and/or auxiliarybarrier layer(s), e.g. one or more water barrier layer(s) and one ormore jacketing layer(s).

Due to benefits, mentioned herein, which are achievable withcrosslinking, the insulating layer and the semiconducting layers incable applications are typically made using crosslinkable polymercompositions. The polymer compositions in a formed layered cableapplication are then crosslinked.

Furthermore, such crosslinkable polymer compositions comprising lowdensity polyethylene (LDPE), are today among the predominant cableinsulating materials for power cables.

The crosslinking can be performed with crosslinking agents where thecrosslinking agents decompose generating free radicals. Suchcrosslinking agents, e.g. peroxides, are conventionally added to thepolymeric material prior to, or during, the extrusion of the cable. Saidcrosslinking agent should preferably remain stable during the extrusionstep. The extrusion step should preferably be performed at a temperaturelow enough to minimize the early decomposition of the crosslinkingagent, but high enough to obtain proper melting and homogenisation ofthe polymer composition. If a significant amount of crosslinking agent,e.g. peroxide, decomposes already in the extruder, and thereby initiatespremature crosslinking, it will result in formation of, so-called,“scorch”, i.e. inhomogeneity, surface unevenness and possiblydiscolouration in the different layers of the resultant cable.Therefore, any significant decomposition of crosslinking agents, i.e.free radical forming agents, during extrusion should be avoided.Instead, the crosslinking agents should ideally decompose merely in asubsequent crosslinking step at elevated temperature. The elevatedtemperature will increase the decomposition rate of the crosslinkingagents and will thus increase crosslinking speed, and a desired, i.e. atarget, crosslinking degree may be reached faster.

Moreover, when a polymer composition in, for example, a cable, iscrosslinked, the decomposition of the crosslinking agents, e.g.peroxides, during the crosslinking, will further also result information of peroxide decomposition products. Some of the peroxidedecomposition products are volatile, and their main component is methaneif the types of peroxides that typically are used for crosslinking inrelation to, for example, a cable, are used. The peroxide decompositionproducts remain mostly captured within the polymer composition of, forexample, a cable, after crosslinking. This causes, e.g. problems in viewof the cable manufacturing process as well as in view of the quality ofthe final cable.

Especially MV, HV and EHV power cables must have layers of high qualityin order to help safety during installation and in end uses of saidcables. In installation, for example, it is of importance to avoid thatcaptured decomposition products e.g. flammable methane, ignite, forexample when end caps are removed. In service, volatile peroxidedecomposition products formed in a cable during a crosslinking step cancreate a gas pressure and thus cause defects in the shielding and in thejoints. E.g. when a cable core is equipped with a metal barrier, thenthe gaseous products can exert a pressure, especially on the joints andterminations, whereby a system failure may occur. Thus, the level ofthese volatile peroxide decomposition products needs to be reduced, to alow enough level, before subsequent cable production steps can takeplace.

A low enough level of the volatile peroxide decomposition productsrenders a use of the polymer composition comprising LDPE safe for use ininstallations, such as cable installations, and with accessories, suchas cable accessories. Thus, today a, so called, degassing step, whichreduces the volatile peroxide decomposition products, is needed in cableproduction. The degassing step is a time and energy consuming and thuscostly operation in a cable manufacturing process. Degassing requireslarge heated chambers which must be well ventilated to avoid thebuild-up of e.g. flammable methane. The cable core, i.e. layers andconductor, typically wound to cable drums, is normally held in saiddegassing step in elevated temperature in the range of 50-80° C., e.g.60-70° C., for lengthy time periods. When exposed to the requiredtemperatures thermal expansion and softening of the insulation can occurand lead to unwanted deformation of the formed cable layers resultingdirectly to failures of the cable. The degassing of HV and EHV cableswith high cable weight needs thus often to be carried out at decreasedtemperatures which prolongs the degassing time further. Accordingly,there is a need to find new solutions to overcome the problems of thestate of the art.

Further, the crosslinking of a polymer composition, comprised, in, forexample, a cable, substantially contributes, to the improved heat anddeformation resistance, mechanical strength, chemical resistance andabrasion resistance of the polymer composition and the cable comprisingthe polymer composition.

In this context see U.S. Pat. No. 5,539,075, which relates to a methodof producing an unsaturated copolymer of ethylene and at least onemonomer, wherein the monomer is a polyunsaturated compound andcopolymerisable with ethylene.

See also EP2318210B1, which relates to a polymer composition comprisingan unsaturated LDPE copolymer of ethylene with one or morepolyunsaturated comonomers and being suitable for crosslinked polymerapplications. The polymer composition has a melt flow rate under 2.16 kgload, MFR₂, of at least 2.8 g/10 min, and contains carbon-carbon doublebonds in an amount of at least 0.40 carbon-carbon double bonds/1000carbon atoms.

Additionally, different materials, i.e. polyethylenes and polymercompositions comprising polyethylenes, may be needed for differentcables, cable constructions and lines. Moreover, it is not possible torun all cables or cable constructions on all cable lines using, a,herein so called, standard viscosity “crosslinked” (here, morecorrectly, meaning “crosslinkable”) polyethylene (XLPE) materials havingmelt flow rate under 2.16 kg load, MFR₂, values around 2 g/10 min. Thatis because of that these standard viscosity XLPE materials do not havesufficient sagging resistance. The insufficiency in sagging resistanceis normally solved, in the case of a cable, by using materials with MFR₂values lower than 2 g/10 min. Materials, which have MFR₂ values lowerthan 2 g/10 min, have high viscosity and improved sagging resistance.The improved sagging resistance is needed for big cable constructionsand for cable production in catenary cable lines, as well as, for cableproduction in horizontal cable lines. For example, in horizontalcontinuous vulcanization lines, e.g. a Mitsubishi Dainichi ContinuousVulcanization (MDCV) line, and in catenary continuous vulcanization(CCV) lines (especially for thicker constructions) for producing cables,it is typically required to use polymeric materials, e.g., forinsulation layers, which have lower MFR₂ compared to the MFR₂ ofpolymeric materials (e.g. standard viscosity XLPE materials) used invertical continuous vulcanization (VCV) lines and CCV lines (for thinnerconstructions).

In horizontal continuous vulcanization lines for producing cables, theconductor may sink within the insulation layer, if polymeric materialswhich have a too high MFR₂ are used, the sinking of the conductor mayalso result in an eccentricity of the cable core.

Likewise in CCV lines, if polymeric materials which have a too highMFR₂, i.e. also having a too low sagging resistance, are used, the wallthickness may become too large as soft molten polymeric material of aninsulation layer may drop off the conductor. This will result in adownward displacement of the insulation layer, thus rendering aneccentricity, e.g. a, so called, pear shaped cable core.

Further, the insufficiency in the sagging resistance may be counteractedby different methods, such as:

-   -   using eccentric tools in the extruder head to compensate for the        effect of sinking of the conductor;    -   twisting of the cable core to counter act displacement of the        conductor, using of a double rotating technique to counteract        the pear shaping, and, also, using a, so-called, entry heat        treatment (EHT).

Accordingly, polymeric materials having a comparably lower MFR₂ andhigher viscosity, as already described, are normally used to counteractthese sagging behaviors.

However, materials having high viscosity will generate a higher melttemperature at commonly used extrusion conditions which may lead tohigher risk for premature crosslinking and, thus, formation ofprematurely crosslinked matter, i.e. “scorch”. “Scorch” may, as alreadydescribed herein, be inhomogeneity, surface unevenness and/or possiblydiscolouration in the different layers of, for example, the resultingcable. The formation of “scorch” may have severe impact onproductivities in the cable lines, as it significantly limits theproduction length before cleaning is needed and therefore the productionrate is reduced. Thus, when producing a cable, by using polymericmaterials having a lower MFR₂ generating a higher temperature in themelt, a lower production speed is required to reduce the melttemperature and thereby minimizing “scorch”.

Accordingly, a drawback with decreasing the MFR₂ value of a material maythus be that it also requires changes in processing conditions such asthe lowering of the production speed.

The processing conditions are, besides the sagging resistance, alsoproperties that are of importance in relation to crosslinkable XLPEmaterials, such as peroxide crosslinkable XLPE materials. Ideally, thematerial shall have low viscosity under the extrusion step of theprocess in order to have an, under the extrusion step, desirably lowmelt temperature. On the other hand, in the crosslinking step of theprocess a comparably higher viscosity of the material may be desirable.If a crosslinkable XLPE material generates a low melt temperature, thereis less risk for “scorch” formation during an extrusion of, e.g., acable construction, as compared with an extrusion involving anothercrosslinkable XLPE material generating a higher temperature in the melt.

The sagging resistance and the viscosity under processing conditions mayboth be visualised by viscosity curves obtained in plate-plate rheologymeasurements. Said sagging resistance is, then, visualised via thecomplex viscosity (η*) at very low shear rates, i.e. η*₀ and η*_(0.05)at 0 rad/sec and 0.05 rad/sec, respectively, and said viscosity underprocessing conditions is, then, visualised via the complex viscosityη*₃₀₀ at 300 rad/sec.

Still a further important property for XLPE is the crosslinking degreewhere a target crosslinking degree level shall be reached with,optimally, as low amount of crosslinking agent, such as peroxide, aspossible. The degree of crosslinking may, for example, be measured withthe, so-called, hot set test. In accordance with said hot set test, thelower the hot set elongation value, the more crosslinked is thematerial. An, as low as possible, amount of the crosslinking agentreduces the volatile peroxide decomposition products and also reducestime needed for degassing.

The extrusion and the crosslinking steps of a polymeric materialincluded in, for example, cable production have different requirements.The critical parameter for the extrusion step is, as already described,that the polymeric material generates a low melt temperature in order toreduce the risk for “scorch”. This is governed by the rheologicalproperties in the region of shear rate that the polymeric material isexhibiting in the extruder, for example, using a low complex viscosity(η*) at 300 rad/sec. The low complex viscosity (η*) at 300 rad/sec isgenerally connected to a polymeric material having a higher melt flowrate (MFR₂).

However, an increase in melt flow rate must often be balanced as apolymeric material with a high MFR₂ has a too low sagging resistancewhich will result in, for example, a non-centric cable, which is notacceptable. The rheological property that is influencing the saggingresistance is the complex viscosity (η*) at very low shear rates, suchas, at 0 rad/sec. However, the complex viscosity (η*) at 0 rad/sec is anextrapolated value, and thus here a measured complex viscosity (η*) at0.05 rad/sec is used instead.

Accordingly, there is a need to find new solutions to overcome theproblems of the state of the art.

DESCRIPTION OF THE INVENTION

The present invention relates to a polyethylene, wherein thepolyethylene has a melt flow rate at 2.16 kg loading (MFR₂), determinedaccording to method ISO 1133-1:2011, which MFR₂ is A g/10 min andA₁≤A≤A₂; wherein A₁ is 0.5 and A₂ is 1.70, and contains a total amountof vinyl groups which is B vinyl groups per 1000 carbon atoms, and B₁≤B,wherein B₁ is 0.45, determined according to method ASTM D6248-98.

According to the present invention the polyethylene has a melt flow rateat 2.16 kg loading (MFR₂), which MFR₂ is A g/10 min and A₁≤A≤A₂; whereinA₁ is 0.5 and A₂ is 1.70, when determined according to method ISO1133-1:2011, see some details of method ISO 1133-1:2011 in Melt FlowRate under Determination Methods herein.

Further, the polyethylene of the present invention contains a totalamount of vinyl groups which is B vinyl groups per 1000 carbon atoms,and B₁≤B, wherein B₁ is 0.45, determined according to method ASTMD6248-98, see details with regard to method ASTM D6248-98 underDetermination Methods herein.

The polyethylene, as described herein, comprises vinyl groups, forexample, allyl groups. Vinyl groups are functional groups which comprisecarbon double bonds. Further, the polyethylene may in addition compriseother functional groups also comprising carbon carbon double bonds. Theother functional groups, also comprising carbon carbon double bonds, maybe, e.g., vinylidene groups and/or vinylene groups. The vinylene grouphas either a cis or trans configuration.

The polyethylene according to the present invention, as defined herein,surprisingly combines, in one polymer, i.e. in the polyethyleneaccording to the present invention:

good processability, e.g. a good flowability which is generally onlyassociated with polymers having a comparably higher MFR₂, with excellentsagging resistance generally only associated with polymers having acomparably lower MFR₂.

Further, that the polymer, i.e. said polyethylene, combines excellentsagging properties with good processability, e.g. flowability, is alsoillustrated by the fact that the polyethylene exhibits balanced complexviscosities (η*) at 300 rad/sec and at 0.05 rad/sec, both complexviscosities (η*) are determined according to method ISO 6721-1 onstabilised samples of the polyethylene. The complex viscosity (η*) at300 rad/sec is accordingly low, and the complex viscosity (η*) at 0.05rad/sec is accordingly high, which results in a polymer, i.e. saidpolyethylene, which has improved processing properties in an extruder,and which still allows generation of a cable, including big cableconstructions, with good centricity in cable production for all types ofcable lines. Such cables, comprising layers, e.g. insulation layers,being obtained from the polyethylene, may thus accordingly be produced.

Moreover, besides, surprisingly exhibiting the combination excellentsagging properties with good processability, the polyethylene, accordingto the present invention, has unexpectedly also been shown to enablethat a technically desirable level of crosslinking degree is maintainedwhen using crosslinking agents, e.g. peroxides, which are well known inthe art, i.e. a technically more desirable level of crosslinking degreein comparison with polyethylenes containing a lower total amount ofvinyl groups.

Thus, the polyethylene of the present invention is clearly highlyadvantageous to be used in, for example, production of crosslinkable andcrosslinked articles, for example cables, e.g. cable layers thereof, forexample, cable insulation layers.

The polyethylene is suitably used to obtain a polymer composition. Saidpolymer composition, obtained by using the polyethylene, may becrosslinkable and may thus be highly suitable for producingcrosslinkable articles, e.g. one or more crosslinkable layers of acable, for example one or more crosslinkable insulation layers, of acable, which layers are subsequently crosslinked.

“Crosslinkable” is a well known expression and means that the polymercomposition can be crosslinked, e.g. via radical formation, to formbridges i.a. amongst the polymer chains.

The polyethylene, according to the present invention, which has thecomparably lower MFR₂, A, has surprisingly been shown to have animproved crosslinking response in comparison with polyethylenes having acomparably higher MFR₂, at similar vinyl content.

Said “total amount of vinyl groups which is B vinyl groups per 1000carbon atoms” means the “total amount of vinyl groups which is B vinylgroups per 1000 carbon atoms” present in the polyethylene in accordancewith the present invention when measured prior to any crosslinking.

The method ASTM D6248-98 for determining the amount of the vinyl groupsare described under “Determination Methods”.

The MFR₂ is determined according to ISO 1133-1:2011 under 2.16 kg load.The determination temperature is chosen, as well known, depending on thetype of the polymer used.

The herein exemplified subgroups of the herein described properties,further features, such as further properties or ranges thereof, andexemplified embodiments apply generally to said polyethylene as well asto a polymer composition obtained from the polyethylene, or comprisingthe polyethylene, to end applications and to any processes thereof, andcan be combined in any combination.

In embodiments of the present invention, the polyethylene, as describedherein, contains B vinyl groups per 1000 carbon atoms, as describedherein, wherein B≤B₂, and B₂ is 3.0.

In further embodiments of the present invention, the polyethylene, asdescribed herein, contains a comparably higher total amount of vinylgroups, B, as defined herein.

Note that the wordings “embodiment” or “embodiments”, even if standingalone herein, always relate embodiment of the present invention orembodiments of the present invention.

In a further embodiment, B₁ is 0.46.

Still a further embodiment of the polyethylene is disclosed, wherein B₁is 0.48.

A further embodiment of the polyethylene is disclosed, wherein B₁ is0.50.

An even further embodiment of the polyethylene is disclosed, wherein B₁is 0.52.

Further embodiments of the polyethylene are disclosed, wherein B₁ is0.53 or 0.54.

An even further embodiment of the polyethylene is disclosed, wherein B₁is 0.55.

Still a further embodiment of the polyethylene is disclosed, wherein B₁is 0.56.

A further embodiment of the polyethylene is disclosed, wherein B₁ is0.58.

Still a further embodiment of the polyethylene is disclosed, wherein B₂is 3.0.

A further embodiment of the polyethylene is disclosed, wherein B₁ is0.58 and/or B≤B₂, and B₂ is 3.0.

An even further embodiment of the polyethylene is disclosed, wherein B₁is 0.60.

Further embodiments of the polyethylene are disclosed, wherein B₁ is0.60, 0.65 or 0.70.

Still further embodiments of the polyethylene are disclosed, wherein B₁is 0.61, 0.66, 0.71, 0.75, 0.80, 0.82 or 0.84.

Even further embodiments of the polyethylene are disclosed, wherein B₁is 0.75, 0.80, 0.82 or 0.84.

Still a further embodiment of the polyethylene is disclosed, wherein B₁is 0.82.

An even further embodiment of the polyethylene is disclosed, wherein B₁is 0.84.

Still a further embodiment of the polyethylene is disclosed, wherein B₁is 0.86.

In a further embodiment, the polyethylene contains a total amount ofvinyl groups (B), wherein B₁ is 0.88.

The “amount of vinyl groups” means in this embodiment the “total amountof vinyl groups present in the polyethylene”. The term “vinyl group” asused herein takes its conventional meaning, i.e. the moiety “—CH═CH₂”.Further, the polyethylene may in addition comprise other functionalgroups also comprising carbon carbon double bonds. The other functionalgroups, also comprising carbon carbon double bonds, may be, e.g.,vinylidene groups and/or vinylene groups. The vinylene group has eithera cis or trans configuration. For the avoidance of doubt, vinylidenegroups and vinylene groups are not vinyl groups as the terms are usedherein. The polyethylene means herein both homopolymer, having beenprovided with unsaturation by a chain transfer agent, and a copolymer,wherein the unsaturation is provided by polymerising a monomer togetherwith at least a polyunsaturated comonomer, optionally in the presence ofa chain transfer agent and, also, optionally in combination with furthercomonomers.

In one embodiment the polyethylene is an unsaturated copolymer which, asalready mentioned herein, comprises one or more polyunsaturatedcomonomer(s).

Further, said vinyl groups (B) present in the unsaturated copolymer mayoriginate from said polyunsaturated comonomer, a process of producingthe polyethylene and, optionally, from any used chain transfer agent.

When the polyethylene of the polymer composition, is an unsaturatedcopolymer comprising at least one polyunsaturated comonomer, then thepolyunsaturated comonomer is straight carbon chain with at least 8carbon atoms and at least 4 carbon atoms between the non-conjugateddouble bonds, of which at least one is terminal.

As to suitable polymer materials for the polymer composition, saidpolyethylene can be any polymer having relevant features, as definedherein, for the polyethylene of the exemplified polymer composition. Thepolyethylene may be selected from homopolymers of polyethylene as wellas copolymers of polyethylene with one or more comonomer(s). Thepolyethylene can be unimodal or multimodal with respect to molecularweight distribution and/or comonomer distribution, which expressionshave a well known meaning.

In one embodiment, the polyethylene is a homopolymer of ethylene.

In an embodiment of the present invention, a polymer composition isdisclosed which is obtained by a process comprising the polyethylene.

In an exemplified embodiment the polyethylene is an unsaturatedcopolymer of polyethylene with at least one polyunsaturated comonomerand optionally with one or more other comonomer(s).

Said unsaturated copolymer of polyethylene is an unsaturated copolymerof ethylene.

In an embodiment of the present invention, a polyethylene, as describedherein, is disclosed, which is a copolymer of a monomer with at leastone polyunsaturated comonomer and with zero, one or more, for example,zero, one, two or three, other comonomer(s), and wherein said totalamount of vinyl groups (B) present in the polyethylene include vinylgroups originating from said at least one polyunsaturated comonomer,e.g. diene.

In an exemplified embodiment the polyethylene is obtained by a processcomprising an unsaturated copolymer of ethylene.

Said copolymer of ethylene may be a LDPE copolymer produced in a highpressure polymerisation process, wherein ethylene is copolymerised withat least one polyunsaturated comonomer and optionally with one or moreother comonomer(s), optionally in the presence of a chain transferagent.

The optional further comonomer(s) present in the polyethylene, forexample, copolymer of ethylene, is different from the “backbone” monomerand may be selected from an ethylene and higher alpha-olefin(s), e.g.C₃-C₂₀ alpha-olefin(s), for example, a cyclic alpha-olefin of 5 to 12carbon or a straight or branched chain alpha-olefin of 3 to 12 carbonatoms, such as propylene, 1-butene, 1-hexene, 1-nonene or 1-octene, aswell as, from polar comonomer(s).

In one embodiment the straight or branched chain alpha-olefin is astraight or branched chain alpha-olefin of 3 to 6 carbon atoms.

In a further embodiment the straight chain alpha-olefin is propylene.

It is well known that e.g. propylene can be used as a comonomer or as achain transfer agent (CTA), or both, whereby it can contribute to thetotal amount of the vinyl groups, B. Herein, when copolymerisable CTA,such as propylene, is used, the copolymerised CTA is not calculated tothe comonomer content.

In an exemplified embodiment, the polyethylene is an unsaturated LDPEpolymer, for example, an unsaturated LDPE copolymer comprising at leastone comonomer which is a polyunsaturated comonomer (referred herein asLDPE copolymer).

Further, said polyunsaturated comonomer may be a diene, for example, (1)a diene which comprises at least 8 carbon atoms, the first carbon-carbondouble bond being terminal and the second carbon-carbon double bondbeing non-conjugated to the first one (group 1 dienes). Exemplifieddienes (1) may be selected from C₈ to C₁₄ non-conjugated dienes ormixtures thereof, for example, selected from 1,7-octadiene,1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene,7-methyl-1,6-octadiene, 9-methyl-1,8-decadiene, or mixtures thereof. Ina further embodiment, the diene (1) is selected from 1,7-octadiene,1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, or any mixturethereof.

A further embodiment according to the present invention as describedherein, is disclosed, wherein the polyethylene is a copolymer of amonomer with at least one polyunsaturated comonomer, wherein thepolyunsaturated comonomer is a straight carbon chain with at least 8carbon atoms and at least 4 carbon atoms between the non-conjugateddouble bonds, of which at least one is terminal, for example, C₈ to C₁₄non-conjugated diene, e.g. selected from 1,7-octadiene, 1,9-decadiene,1,11-dodecadiene, 1,13-tetradecadiene, or mixtures thereof.

In a preferred embodiment the polyethylene is a copolymer of ethyleneand 1,7-octadiene.

Still a further embodiment according to the present invention, asdescribed herein, is disclosed, wherein the polyethylene is anunsaturated LDPE homopolymer or copolymer, e.g. a LDPE copolymer ofethylene with one or more polyunsaturated comonomer(s) and with zero,one or more other comonomer(s).

In addition or as an alternative to the dienes (1) listed herein, thediene may also be selected from other types of polyunsaturated dienes(2), such as from one or more siloxane compounds having the followingformula (group (2) dienes):CH₂═CH—[SiR₁R₂—O]_(n)—SiR₁R₂—CH═CH₂,

-   -   wherein n=1 to 200, and    -   R₁ and R₂, which can be the same or different, are selected from        C₁ to C₄ alkyl groups and/or C₁ to C₄ alkoxy groups.

Further, R₁ and/or R₂ may, for example, be methyl, methoxy or ethoxy.Furthermore, n may, for example, be 1 to 100, e.g., 1 to 50. As anexample, divinylsiloxanes, for example, α,ω-divinylsiloxane can bementioned.

Exemplified polyunsaturated comonomers for the polyethylene are thedienes from group (1) as defined herein. The polyethylene may, forexample, be a copolymer of ethylene with at least one diene selectedfrom 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene,1,13-tetradecadiene, or any mixture thereof, and optionally with one ormore other comonomer(s). It is also exemplified that said polyethyleneis the herein-mentioned unsaturated LDPE copolymer. It may comprisefurther comonomers, e.g. polar comonomer(s), alpha-olefin comonomer(s),non-polar comonomer(s) or any mixture thereof.

As a polar comonomer, compound(s) containing hydroxyl group(s), alkoxygroup(s), carbonyl group(s), carboxyl group(s), ether group(s) or estergroup(s), or a mixture thereof can used.

Further, a non-polar comonomer, is/are compound(s) not containinghydroxyl group(s), alkoxy group(s), carbonyl group(s), carboxylgroup(s), ether group(s) nor ester group(s).

In a further embodiment, compounds containing carboxyl and/or estergroup(s) are used and, e.g., the compound is selected from the groups ofacrylate(s), methacrylate(s) or acetate(s), or any mixtures thereof.

If present in said unsaturated LDPE copolymer, the polar comonomer may,for example, be selected from the group of alkyl acrylates, alkylmethacrylates or vinyl acetate, or a mixture thereof. Further, saidpolar comonomers may, for example, be selected from C₁- to C₆-alkylacrylates, C₁- to C₆-alkyl methacrylates or vinyl acetate. Stillfurther, said polar copolymer comprises a copolymer of ethylene with C₁-to C₄-alkyl acrylate, such as methyl, ethyl, propyl or butyl acrylate,or vinyl acetate, or any mixture thereof. Still further, said polarcopolymer preferably comprises a copolymer of ethylene with C₁- toC₄-alkyl acrylate, such as methyl, ethyl, propyl or butyl acrylate, orany mixture thereof.

The polyethylene, useful in e.g. any herein described polymercomposition, can be prepared using i.a. any conventional polymerisationprocess and equipment, the conventional means as described herein forproviding unsaturation and any conventional means for adjusting theMFR₂, in order to control and adjust the process conditions to achieve adesired balance between MFR₂ and amount of vinyl groups of thepolymerised polymer. The unsaturated LDPE polymer as defined herein,e.g. the unsaturated LDPE copolymer, may be produced in high pressurereactor by free radical initiated polymerisation (referred to as highpressure radical polymerisation). The usable high pressure (HP)polymerisation and the adjustment of process conditions are well knownand described in the literature, and can readily be used by a skilledperson to provide the herein described inventive balance. High pressurepolymerisation can be performed in a tubular reactor or an autoclavereactor, e.g. in a tubular reactor. One embodiment of HP process isdescribed herein for polymerising ethylene optionally together with oneor more comonomer(s), for example, at least with one or morepolyunsaturated comonomer(s), in a tubular reactor to obtain a LDPEhomopolymer or copolymer as defined herein. The process can be adaptedto other polymers as well.

Further, the polyethylene may be produced in a high pressure reactor byfree radical polymerisation (referred to as high pressure radicalpolymerisation). Free radical initiated polymerisation is very rapid andthus well suited for a continuous process where careful control ofprocess parameters can be obtained by continuous monitoring andadjustments. To the high pressure radical polymerisation process thereis a continuous feed of ethylene and initiator. The high pressureradical polymerisation process is preferably an autoclave or tubularprocess, more preferably a tubular reactor. A high pressure tubularprocess typically produces a polyethylene with a more narrow molecularweight distribution and with a lower degree of long chain branches andwith another branching structure compared to a polyethylene produced inan autoclave process if similar process conditions are used such assimilar temperature profile, similar pressure and similar initiatorfeed. Typically, a tubular reactor also has more favourable productioneconomics because they have higher ethylene conversion rates.

In a further embodiment the polyethylene of the present invention isproduced in a continuous high pressure tubular reactor.

Compression:

Ethylene is fed to a compressor mainly to enable handling of highamounts of ethylene at controlled pressure and temperature. Thecompressors are usually a piston compressor or diaphragm compressors.The compressor is usually a series of compressors that can work inseries or in parallel. Most common is 2-5 compression steps. Recycledethylene and comonomers can be added at feasible points depending on thepressure. Temperature is typically low, usually in the range of lessthan 200° C. or less than 100° C. Said temperature may, for example, beless than 200° C.

Tubular Reactor:

The mixture is fed to the tubular reactor. First part of the tube is toadjust the temperature of the fed ethylene; usual temperature is150-170° C. Then the radical initiator is added. As the radicalinitiator, any compound or a mixture thereof that decomposes to radicalsat an elevated temperature can be used. Usable radical initiators arecommercially available. The polymerisation reaction is exothermic. Therecan be several radical initiator injections points, e.g. 1-5 points,usually provided with separate injection pumps. Also ethylene andoptional comonomer(s) can be added at any time during the process, atany zone of the tubular reactor and/or from one or more injectionpoints, as well known. The reactor is continuously cooled e.g. by wateror steam. The highest temperature is called peak temperature and thelowest temperature is called radical initiator temperature. The “lowesttemperature” means herein the reaction starting temperature which iscalled the initiation temperature which is “lower” as evident to askilled person.

Suitable temperatures range from 80 to 350° C. and pressure from 100 to400 MPa. Pressure can be measured at least in the compression stage andafter the tube. Temperature can be measured at several points during allsteps. High temperature and high pressure generally increase output.Using various temperature profiles selected by a person skilled in theart will allow control of structure of polymer chain, i.e. Long ChainBranching and/or Short Chain branching, density, MFR, viscosity,Molecular Weight Distribution etc.

The reactor ends conventionally with a valve. The valve regulatesreactor pressure and depressurizes the reaction mixture from reactionpressure to separation pressure.

Separation:

The pressure is typically reduced to approx. 10 to 45 MPa, for exampleto approx.

30 to 45 MPa. The polymer is separated from the unreacted products, forinstance gaseous products, such as monomer or the optional comonomer(s),and most of the unreacted products are recovered. Normally low molecularcompounds, i.e. wax, are removed from the gas. The pressure can furtherbe lowered to recover and recycle the unused gaseous products, such asethylene. The gas is usually cooled and cleaned before recycling.

Then the obtained polymer melt is normally mixed and pelletized.Optionally, or in some embodiments, additives can be added in the mixer.Further details of the production of ethylene (co)polymers by highpressure radical polymerisation can be found in the Encyclopedia ofPolymer Science and Engineering, Vol. 6 (1986), pp 383-410.

The MFR₂ of the polyethylene, e.g. LDPE copolymer, can be adjusted byusing e.g. chain transfer agent(s) during the polymerisation, and/or byadjusting reaction temperature or pressure. When the LDPE copolymer ofthe invention is prepared, then, as well known, the amount of vinylgroups can be adjusted by polymerising the ethylene e.g. in the presenceof one or more polyunsaturated comonomer(s), chain transfer agent(s), orboth, using the desired feed ratio between ethene and polyunsaturatedcomonomer and/or chain transfer agent, depending on the nature andamount of carbon carbon double bonds desired for the LDPE copolymer.I.a. WO 9308222 describes a high pressure radical polymerisation ofethylene with polyunsaturated monomers, such as an α,ω-alkadienes, toincrease the unsaturation of an ethylene copolymer. The non-reacteddouble bond(s) thus provides pendant vinyl groups to the formed polymerchain at the site, where the polyunsaturated comonomer was incorporatedby polymerisation. As a result the unsaturation can be uniformlydistributed along the polymer chain in random copolymerisation manner.Also e.g. WO 9635732 describes high pressure radical polymerisation ofethylene and a certain type of polyunsaturated α,ω-divinylsiloxanes.Moreover, as known, e.g. propylene can be used as a chain transfer agentto provide double bonds, whereby it can also partly be copolymerisedwith ethylene.

The alternative unsaturated LDPE homopolymer may be produced analogouslyto the herein described process conditions as the unsaturated LDPEcopolymer, except that ethylene is polymerised in the presence of achain transfer agent only.

One exemplified polyethylene, e.g. of the LDPE copolymer, of the presentinvention may have a density, when measured on the polyethyleneaccording to ISO 1183-1 method A:2012, of e.g. higher than 0.860 g/cm³,higher than 0.870, higher than 0.880, higher than 0.885, higher than0.890, higher than 0.895, higher than 0.900, higher than 0.905, higherthan 0.910, or of higher than 0.915 g/cm³.

Another exemplified polyethylene, e.g. of the LDPE copolymer, of thepresent invention may have a density, when measured on the polyethyleneaccording to ISO 1183-1 method A:2012, of up to 0.960 g/cm³, less than0.955, less than 0.950, less than 0.945, less than 0.940, less than0.935, or of less than 0.930 g/cm³.

In a further embodiment the density range, when measured on thepolyethylene according to ISO 1183-1 method A:2012, is from 0.915 to0.930 g/cm³.

Further, said unsaturated copolymer, e.g. the LDPE copolymer, of thepolyethylene comprises comonomer(s) in a total amount of up to 45 wt %,e.g. of from 0.05 to 25 wt %, or e.g. from 0.1 to 15 wt %, based on theamount of the polyethylene. Further, said unsaturated copolymer, e.g.the LDPE copolymer, of the polyethylene preferably comprisescomonomer(s) in a total amount of 0.1 to 5 wt %, based on the amount ofthe polyethylene.

An exemplified polyethylene may be comprised in a polymer composition asdescribed herein, wherein the polymer composition is crosslinkable.

In an exemplified embodiment a polymer composition as described hereinconsists of at least one polyethylene. The polymer composition may alsocomprise further components such as herein described additives which maybe added in a mixture with a carrier polymer, i.e. in so called masterbatch.

In a further embodiment, a polymer composition as described herein maycomprise the polyethylene, as described herein, together with acrosslinking agent and together with 0, 1, 2, 3, 4, 5, 6 or moreadditive(s), and wherein the polymer composition is in the form ofpellets.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, discloses the polyethylene containing atotal amount of vinyl groups which is B vinyl groups per 1000 carbonatoms, and B₁≤B, wherein B₁ is 0.89, when measured prior to crosslinkingaccording to method ASTM D6248-98.

Still a further embodiment of the polyethylene is disclosed, wherein B₁is 0.90.

An even further embodiment of the polyethylene is disclosed, wherein B₁is 0.94.

Still a further embodiment of the polyethylene is disclosed, wherein B₁is 0.95.

An even further embodiment of the polyethylene is disclosed, wherein B₁is 1.00.

Further embodiments of the polyethylene are disclosed, wherein B₁ is0.95, 1.00, 1.05 or 1.10.

Still further embodiments of the polyethylene are disclosed, wherein B₁is 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25 or 1.30.

Even further embodiments of the polyethylene are disclosed, wherein B₁is 1.15, 1.20, 1.25 or 1.30.

Still a further embodiment of the polyethylene is disclosed, wherein B₁is 1.05.

An even further embodiment of the polyethylene is disclosed, wherein B₁is 1.10.

Still a further embodiment of the polyethylene is disclosed, wherein B₁is 1.15.

An even further embodiment of the polyethylene is disclosed, wherein B₁is 1.20.

A further embodiment of the polyethylene is disclosed, wherein B₁ is1.25.

Still a further embodiment of the polyethylene is disclosed, wherein B₁is 1.30.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein B≤B₂ and B₂ is3.0.

Further embodiments of the polyethylene are disclosed wherein thepolyethylene contains a total amount of vinyl groups which is B vinylgroups per 1000 carbon atoms, and B₁≤B≤B₂, wherein B₁ and B₂ may each beselected from any of the values given herein for B₁ and B₂,respectively.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein B₂ is 2.5.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein B₂ is 2.0.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein B₂ is 1.8.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein B₂ is 1.7.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein B₂ is 1.6.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein B₂ is 1.5.

The MFR₂ is determined, prior to any crosslinking, according to ISO1133-1:2011 under 2.16 kg load and at 190° C.

Further embodiments of the polyethylene are disclosed which have a meltflow rate, MFR₂, which is A g/10 min and A₁≤A≤A₂; wherein A₁ and A₂ mayeach be selected from any of the values given herein for A₁ and A₂,respectively.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein A₁ is 0.55.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein A₁ is 0.60.

Still an embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein A₁ is 0.65.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein A₁ is 0.70.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein A₁ is 0.75.

Still an embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein A₁ is 0.80.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein A₁ is 0.85.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein A₁ is 0.90.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein A₂ is 1.65, 1.60, 1.55 or 1.50.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein A₂ is 1.65.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein A₂ is 1.60.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein A₂ is 1.65 or1.60.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein A₂ is 1.55.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein A₂ is 1.50.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein A₂ is 1.55 or1.50.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein the polyethylenehas a complex viscosity (η*) at 0.05 rad/sec, which is X Pas, andX₁≤X≤X₂, wherein X₁ is 10000 and X₂ is 30000, and

a complex viscosity (η*) at 300 rad/sec, which is Y Pas, and Y₁≤Y≤Y₂,wherein Y₁ is 5 and Y₂ is 350, both complex viscosities (η*) aredetermined according to method ISO 6721-1 on stabilised samples of thepolyethylene.

The complex viscosity (η*) at 0.05 rad/sec, which is X Pas, herevisualises the sagging resistance, and the complex viscosity (η*) at 300rad/sec, which is Y Pas, here visualises the viscosity under processingconditions.

Further embodiments of the polyethylene are disclosed wherein thepolyethylene has a complex viscosity (η*) at 0.05 rad/sec, determinedaccording to method ISO 6721-1 on stabilised samples of thepolyethylene, which is X Pas, and X₁≤X≤X₂, wherein X₁ and X₂ may each beselected from any of the values given herein for X₁ and X₂,respectively.

Still further embodiments of the polyethylene are disclosed wherein thepolyethylene has a complex viscosity (η*) at 300 rad/sec determinedaccording to method ISO 6721-1 on stabilised samples of thepolyethylene, which is Y Pas, and Y₁≤Y≤Y₂, wherein Y₁ and Y₂ may each beselected from any of the values given herein for Y₁ and Y₂,respectively.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 11000.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 12000.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 13000.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 14000.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 29000.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 28000.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein X₂ is 27000.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 26000.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 25000.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein X₂ is 24000.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 15000.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 16000.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 17000.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 18000.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 18100.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 18200.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein X₁ is 18300.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 18400.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 18500.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 18600.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 18700.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 23500.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 23000.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 22900.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 22800.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 22700.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein X₂ is 22600.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 22500.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 22400.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 22300.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 22000.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein X₂ is 21500.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 21000.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 20500.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 20000.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 19500.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₂ is 19000.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 10.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 20.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 30.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 40.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 50.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 60.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 70.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 80.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 90.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 100.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 110.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 120.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 130.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 140.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 150.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 160.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 170.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 180.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 190.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 200.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 210.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 220.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein Y₁ is 230.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 240.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₁ is 250.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein Y₂ is 345.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₂ is 340.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₂ is 335.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein Y₂ is 330.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₂ is 325.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₂ is 320.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein Y₂ is 315.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₂ is 310.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein Y₂ is 305.

An embodiment of the polyethylene according to the present invention, asdescribed herein, is disclosed, wherein Y₂ is 300.

A further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 12000 and X₂is 28000, and wherein Y₁ is 250 and Y₂ is 330.

Still a further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 13000 and X₂is 27000, and wherein Y₁ is 240 and Y₂ is 340.

An even further embodiment of the polyethylene according to the presentinvention, as described herein, is disclosed, wherein X₁ is 13000 and X₂is 27000, and wherein Y₁ is 250 and Y₂ is 330.

In a particularly preferable embodiment, X₁ is 15500 and X₂ is 24000,and Y₁ is 250 and Y₂ is 330.

A polymer composition obtained from, or comprising, the polyethylene

A polymer composition, obtained from the polyethylene, which may becrosslinkable, is highly suitable for producing crosslinkable articles,e.g. one or more crosslinkable layers of a cable, for example one ormore crosslinkable insulation layers, of a cable, which layers aresubsequently crosslinked.

A further embodiment according to the present invention, as describedherein, is disclosed, wherein a polymer composition is disclosed, whichis crosslinkable or crosslinked, wherein the polymer compositioncomprises, or is obtained from, the polyethylene as described herein.

“Crosslinkable” is a well known expression and means that the polymercomposition, obtained from the polyethylene, can be crosslinked, e.g.via radical formation, to form bridges i.a. amongst the polymer chains.

The term “cable” means herein cable or wire.

The polymer composition obtained from, the polyethylene, or comprisingthe polyethylene, further comprises a crosslinking agent.

Said polymer composition may optionally comprise further component(s)containing vinyl groups, which then also contribute to the amount ofvinyl groups in the polymer composition.

The crosslinking agent is defined herein to be any compound capable togenerate radicals which can initiate a crosslinking reaction. Forexample, the crosslinking agent contains —O—O— bond.

A further embodiment of said polymer composition, as described herein,is disclosed, wherein the crosslinking agent comprises peroxide, i.e.comprises at least one peroxide unit per molecule of crosslinking agent,e.g. a peroxide.

In an even further embodiment, the crosslinking agent comprises aperoxide.

In a further embodiment, the crosslinking agent is a peroxide.

Furthermore, embodiments of said polymer composition, as describedherein, are disclosed, wherein the crosslinking agent, for exampleperoxide, is present in an amount which is Z wt %, based on the totalamount (100 wt %) of the polymer composition, Z≤Z₂, wherein Z₂ is 10, Z₂is 6, Z₂ is 5 or Z₂ is 3.5.

In a further embodiment Z₁≤Z, wherein Z₁ is 0.01.

In further embodiments of the present invention, said polymercomposition, as described herein, is disclosed, wherein Z₁ is 0.02,0.04, 0.06 or 0.08.

Even further, embodiments of said polymer composition according to thepresent invention, as described herein, are disclosed, wherein Z₁ is,for example, 0.1 or 0.2 and/or Z₂ is, for example, 3, or 2.6.

In further embodiments of the present invention, said polymercomposition, as described herein, is disclosed, wherein Z₂ is 2.0, 1.8,1.6 or, alternatively, 1.4.

In still an embodiment the crosslinking agent, for example peroxide, isZ₂ being 1.2.

In still a further embodiments of the present invention, said polymercomposition, as described herein, is disclosed, wherein Z₂ is 1.2, 1.1,1.0 or, alternatively, 0.95.

In still a further embodiment, Z₂ is 1.0.

In a further embodiment Z₂ is 0.98 or 0.96. In still a furtherembodiment Z₂ is 0.98. In an even further embodiment Z₂ is 0.96. In afurther embodiment Z₂ is 0.94, 0.92 or 0.90. In still a furtherembodiment Z₂ is 0.94. In an even further embodiment Z₂ is 0.92. In afurther embodiment Z₂ is 0.90.

In a further embodiment Z₂ is 0.88 or 0.86. In still a furtherembodiment Z₂ is 0.88. In an even further embodiment Z₂ is 0.86. In afurther embodiment Z₂ is 0.84, 0.82 or 0.80. In still a furtherembodiment Z₂ is 0.84. In an even further embodiment Z₂ is 0.82. In afurther embodiment Z₂ is 0.80.

In a further embodiment Z₂ is 0.78 or 0.76. In still a furtherembodiment Z₂ is 0.78. In an even further embodiment Z₂ is 0.76. In afurther embodiment Z₂ is 0.74, 0.72 or 0.70. In still a furtherembodiment Z₂ is 0.74. In an even further embodiment Z₂ is 0.72. In afurther embodiment Z₂ is 0.70.

In an even further embodiment Z₂ is 0.68 or 0.66. In still a furtherembodiment Z₂ is 0.68. In an even further embodiment Z₂ is 0.66. In afurther embodiment Z₂ is 0.64, 0.62 or 0.60. In still a furtherembodiment Z₂ is 0.64. In an even further embodiment Z₂ is 0.62.

The crosslinking agent, for example a peroxide, is present in an amountwhich is Z wt %, based on the total amount (100 wt %) of said polymercomposition, and Z≤Z₂, wherein Z₂ is 0.60.

In a further embodiment Z₂ is 0.58 or 0.56. In still a furtherembodiment Z₂ is 0.58. In an even further embodiment Z₂ is 0.56. In afurther embodiment Z₂ is 0.54, 0.52 or 0.50. In still a furtherembodiment Z₂ is 0.54. In an even further embodiment Z₂ is 0.52. In afurther embodiment Z₂ is 0.50.

In a further embodiment Z₂ is 0.48 or 0.46. In still a furtherembodiment Z₂ is 0.48. In an even further embodiment Z₂ is 0.46.

A further embodiment of said polymer composition according to thepresent invention, as described herein, is disclosed, the amount Z ofthe crosslinking agent, for example a peroxide, is Z₂ being 0.45.

In still a further embodiment the amount Z of the crosslinking agent,for example a peroxide, is Z₂ being 0.40.

In an even further embodiment, the amount Z of the crosslinking agent,for example a peroxide, is Z₂ being 0.35.

Non-limiting examples of the crosslinking agents comprise organicperoxides, such as di-tert-amylperoxide,2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3,2,5-di(tert-butylperoxy)-2,5-dimethylhexane,tert-butylcumylperoxide, di(tert-butyl)peroxide, dicumylperoxide,butyl-4,4-bis(tert-butylperoxy)-valerate,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane,tert-butylperoxybenzoate, dibenzoylperoxide, bis(tertbutylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane,1,1-di(tert-butylperoxy)cyclohexane, 1,1-di(tert amylperoxy)cyclohexane,or any mixtures thereof.

In further embodiments, the crosslinking agent being a peroxide may, forexample, be selected from2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3,2,5-di(tert-butylperoxy)-2,5-dimethylhexane,di(tert-butylperoxyisopropyl)benzene, dicumylperoxide,tert-butylcumylperoxide, di(tert-butyl)peroxide, or any mixturesthereof.

In still a further embodiment the crosslinking agent is a peroxideselected from any of dicumylperoxide,2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3 andtert-butylcumylperoxide, or of any mixtures thereof.

In a further embodiment, the crosslinking agent comprises a peroxidewhich is dicumylperoxide.

In still a further embodiment, the crosslinking agent comprises aperoxide which is 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3.

In even a further embodiment, the crosslinking agent comprises aperoxide which is tert-butylcumylperoxide.

In an embodiment said polymer composition comprises the crosslinkingagent.

In further embodiments said polymer composition may also comprisefurther additive(s). Such further additive(s) comprise:

unsaturated low molecular weight compound(s), for example:

-   -   Crosslinking booster(s) mentioned herein, including any given        specific compound(s), which can contribute to the crosslinking        degree and/or to the amount of vinyl groups in the polymer        composition.    -   One or more scorch retarders (SR) which are defined herein to be        compounds that reduce the formation of scorch during extrusion        of a polymer composition, at typical extrusion temperatures        used, if compared to the same polymer composition extruded        without said compound. The scorch retarders can also contribute        to the amount of vinyl groups in the polymer composition.

The unsaturated low molecular weight compound(s), for example, thecrosslinking booster(s) and/or the “one or more” scorch retarders (SR)may also contribute to the amount of vinyl groups in the polymercomposition.

The crosslinking booster may be a compound containing at least 2,unsaturated groups, such as an aliphatic or aromatic compound, an ester,an ether, an amine, or a ketone, which contains at least 2, unsaturatedgroup(s), such as a cyanurate, an isocyanurate, a phosphate, an orthoformate, an aliphatic or aromatic ether, or an allyl ester of benzenetricarboxylic acid. Examples of esters, ethers, amines and ketones arecompounds selected from general groups of diacrylates, triacrylates,tetraacrylates, triallylcyanurate, triallylisocyanurate,3,9-divinyl-2,4,8,10-tetra-oxaspiro[5,5]-undecane (DVS), triallyltrimellitate (TATM) orN,N,N′,N′,N″,N″-hexaallyl-1,3,5-triazine-2,4,6-triamine (HATATA), or anymixtures thereof. The crosslinking booster can be added in an amount ofsuch crosslinking less than 2.0 wt %, for example, less than 1.5 wt %,e.g. less than 1.0 wt %, for example, less than 0.75 wt %, e.g. lessthan 0.5 wt %, and the lower limit thereof is, for example, at least0.05 wt %, e.g., at least 0.1 wt %, based on the weight of the polymercomposition.

The scorch retarders (SR) may, e.g., be unsaturated dimers of aromaticalpha-methyl alkenyl monomers, such as 2,4-di-phenyl-4-methyl-1-pentene,substituted or unsubstituted diphenylethylene, quinone derivatives,hydroquinone derivatives, monofunctional vinyl containing esters andethers, monocyclic hydrocarbons having at least two or more doublebonds, or mixtures thereof. For example, the scorch retarder may beselected from 2,4-diphenyl-4-methyl-1-pentene, substituted orunsubstituted diphenylethylene, or mixtures thereof.

The amount of scorch retarder may, for example, be equal to, or morethan, 0.005 wt %, based on the weight of the polymer composition.Further, the amount of scorch retarder may, for example, be equal to, ormore than, 0.01 wt %, equal to, or more than, 0.03 wt %, or equal to, ormore than, 0.04 wt %, based on the weight of the polymer composition.

Further, the amount of scorch retarder may, for example, be equal to, orless than, 2.0 wt %, e.g., equal to, or less than, 1.5 wt %, based onthe weight of the polymer composition. Further, the amount of scorchretarder may, for example, be equal to, or less than, 0.8 wt %, equalto, or less than, 0.75 wt %, equal to, or less than, 0.70 wt %, or equalto, or less than, 0.60 wt %, based on the weight of the polymercomposition. Moreover, the amount of scorch retarder may, for example,be equal to, or less than, 0.55 wt %, equal to, or less than, 0.50 wt %,equal to, or less than, 0.45 wt %, or equal to, or less than, 0.40 wt %,based on the weight of the polymer composition.

Still further, the amount of scorch retarder may, for example, be equalto, or less than, 0.35 wt %, e.g., equal to, or less than, 0.30 wt %,based on the weight of the polymer composition. Further, the amount ofscorch retarder may, for example, be equal to, or less than, 0.25 wt %,equal to, or less than, 0.20 wt %, equal to, or less than, 0.15 wt %, orequal to, or less than, 0.10 wt %, based on the weight of the polymercomposition. Moreover, the amount of scorch retarder may, for example,be equal to, or less than, 0.15 wt %, or equal to, or less than, 0.10 wt%, based on the weight of the polymer composition.

Furthermore, the amount of scorch retarder may, for example, be withinthe range of 0.005 to 2.0 wt %, e.g., within the range of 0.005 to 1.5wt %, based on the weight of the polymer composition. Furtherexemplified ranges are e.g. from 0.01 to 0.8 wt %, 0.03 to 0.75 wt %,0.03 to 0.70 wt %, or 0.04 to 0.60 wt %, based on the weight of thepolymer composition. Moreover, exemplified ranges are e.g. from 0.01 to0.60, to 0.55, to 0.50, to 0.45 or, alternatively, to 0.40 wt %, 0.03 to0. 0.55 or, alternatively, to 0.50 wt %, 0.03 to 0.45 or, alternatively,0.40 wt %, or 0.04 to 0.45 or, alternatively, 0.40 wt %, based on theweight of the polymer composition.

Further, the scorch retarders (SR) may, e.g., be selected from graftablestable organic free radicals, as described in EP1699882, which includehindered amine-derived stable organic free radicals: for example,hydroxy-derivative of 2,2,6,6,-tetramethyl piperidinyl oxy (TEMPO), e.g.4-hydroxy-TEMPO or a bis-TEMPO (for example,bis(1-oxyl-2,2,6,6-tetramethylpiperidine-4-yl)sebacate), and, forexample, multi-functional molecules having at least two nitroxyl groupsderived from oxo-TEMPO, 4-hydroxy-TEMPO, an ester of 4-hydroxy-TEMPO,polymer-bound TEMPO, PROXYL, DOXYL, ditertiary butyl N oxyl, dimethyldiphenylpyrrolidine-1-oxyl, or 4 phosphonoxy TEMPO.

The graftable stable organic free radicals may be, as described inEP1699882, present in an amount equal to, or more than, about 0.005weight percent, for example, equal to, or more than, about 0.01 weightpercent and equal to, or more than, about 0.03 weight percent, based onthe weight of the polymer composition.

Further, the graftable stable organic free radicals may be, as describedin EP1699882, present in an amount equal to, or less than, about 20.0weight percent, for example, equal to, or less than, about 10.0 weightpercent, e.g., equal to, or less than, about 5.0 weight percent, basedon the weight of the polymer composition.

Furthermore, the graftable stable organic free radicals may be, asdescribed in EP1699882, present in an amount between about 0.005 weightpercent and about 20.0 weight percent, for example, between 15 about0.01 weight percent and about 10.0 weight percent, e.g., between about0.03 weight percent and about 5.0 weight percent, based on the weight ofthe polymer composition.

Moreover, such further additive(s) comprise additive(s), such asantioxidant(s), stabiliser(s), and/or processing aid(s). As anantioxidant, sterically hindered or semi-hindered phenol(s), aromaticamine(s), aliphatic sterically hindered amine(s), organic phosphate(s),thio compound(s), and mixtures thereof, can be mentioned. As furtheradditive(s), flame retardant additive(s), water tree retardantadditive(s), acid scavenger(s), filler(s) pigment(s), and voltagestabilizer(s) can be mentioned.

Examples of suitable fillers and/or pigments include TiO₂, CaCO₃, carbonblack (e.g. conductive carbon black or “UV black”, i.e. a carbon blackthat absorbs ultraviolet radiation), huntite, mica, kaolin, aluminiumhydroxide (ATH), magnesium dihydroxide (MDH), and SiO₂.

In still a further embodiment said polymer composition according to thepresent invention further comprises fillers and/or pigments.

Furthermore, said fillers and/or pigments may be comprised in saidpolymer composition according to the present invention in amounts of,for example, 0.01 to 5 wt %, e.g., 0.01 to 3 wt % or, e.g., 0.01 to 2 wt%.

Said polymer composition may additionally comprise further polymercomponent(s) including unsaturated polymer(s) and/or polymer(s) that arenot unsaturated, wherein the further polymer component(s) are differentfrom said polyethylene.

Said polymer composition can be provided in the form of a powder orpellets in any shape and size including granules. Pellets can beproduced, e.g. after polymerisation of said polyethylene, in a wellknown manner using the conventional pelletising equipment, such as apelletising extruder. The polymer composition may, for example, beprovided in the form of pellets.

A further embodiment of the present invention discloses a process forproducing a polymer composition as described herein.

Still a further embodiment of the present invention discloses a processfor producing a polyethylene as described herein, or a process forproducing a polymer composition as described herein.

End Applications

An embodiment of the present invention provides an article obtained fromprocess comprising use of a polyethylene as described herein, or of apolymer composition as described herein, wherein the article is, forexample, a cable, e.g. a power cable, for example, a cable layer, ore.g. a power cable layer.

A further embodiment of the present invention provides an articlecomprising layer(s) which is/are obtained from the polyethylene asdescribed herein.

Still a further embodiment of the present invention provides an articlecomprising layer(s), e.g. insulating layer(s), which is/are obtainedfrom the polyethylene as described herein, wherein the article is, forexample, a cable, e.g. a power cable.

A further embodiment of the present invention provides an articlecomprising element(s) which element/s comprising layer(s), e.g.insulating layer(s), which is/are obtained from the polyethylene, asdescribed herein, or from the polymer composition, as described herein.

In a further embodiment of the present invention an article is provided,wherein said article, or the element(s), comprising layer(s), e.g.insulating layer(s), which is/are crosslinkable and is/are obtained fromthe polyethylene, as described herein, or from the polymer composition,as described herein.

In still a further embodiment of the present invention an article isprovided, wherein said article, or the element(s), comprise(s) thepolyethylene as described herein, or the polymer composition, asdescribed herein.

In a further embodiment of the present invention an article is provided,wherein said article, or the element(s), comprising layer(s), e.g.insulating layer(s), which is/are crosslinked and is/are obtained fromthe polyethylene as described herein, or from the polymer composition,as described herein.

In still a further embodiment of the present invention an article isprovided, wherein said article, or the element(s), comprise(s) thepolymer composition as described herein.

In a further embodiment of the present invention an article is provided,wherein said article, or the element(s), comprising layer(s), e.g.insulating layer(s), which is/are crosslinked and is/are obtained fromthe polymer composition as described herein.

A further embodiment of the present invention provides an article, whichis a cable, e.g. a power cable.

Further, the invention is highly suitable for W&C applications, wherebyan article is e.g. a cable, which is crosslinkable and comprises one ormore layers, wherein at least one layer is obtained from thepolyethylene, or the polymer composition, as described herein.

Furthermore, still a further embodiment of the present invention isprovided, wherein said at least one layer comprises the polyethylene, orthe polymer composition, as described herein.

A further embodiment of the present invention provides a power cable,comprising layer(s), e.g. insulating layer(s), which is/are obtainedfrom the polyethylene, or the polymer composition, as described herein.

Still a further embodiment of the present invention is provided, whereinsaid article is an AC power cable.

A further embodiment of the present invention is provided wherein saidarticle is a DC power cable.

Further, the at least one layer of the cable obtained from thepolyethylene, or the polymer composition, is e.g., an insulation layer.

Furthermore, the at least one layer of the cable comprising thepolyethylene, or the polymer composition, may, e.g., be an insulationlayer.

Further, the cable of the present invention may, for example, be a powercable which comprises at least an inner semiconductive layer, aninsulation layer and an outer semiconductive layer in given order,wherein at least the insulation layer is obtained from the polyethylene,or the polymer composition, as described herein.

In a further embodiment the insulation layer comprises the polyethylene,or the polymer composition, as described herein.

The power cable means herein a cable that transfers energy operating atany voltage. The voltage applied to the power cable can be AC, DC ortransient (impulse). In an embodiment, the multi-layered article is apower cable operating at voltages higher than 6 kV.

A further embodiment of the present invention discloses a process forproducing an article, as described herein, which process comprises useof the polyethylene, or the polymer composition, as described herein.

Moreover, the invention provides a process for producing the hereindescribed article, which comprises the steps of a) forming an article,wherein the process comprises the polyethylene, or the polymercomposition, as described herein. Said process may, for example,comprise at least the steps of a₀) meltmixing a polymer composition asdescribed herein optionally together with further component(s), and

a) forming a cable obtained from the polymer composition as describedherein.

A further embodiment discloses forming a cable comprising the polymercomposition as described herein.

“Meltmixing” is well known blending method, wherein the polymercomponent(s) are mixed in an elevated temperature, which is typicallyabove, e.g. at least 20-25° C. above, the melting or softening point ofpolymer component(s).

In an embodiment a cable, which comprises a conductor surrounded by oneor more layers, is produced, wherein the process comprises a step of a)applying on a conductor the polymer composition, as described herein, toform at least one of said layers surrounding the conductor.

Thus in step (a) the at least one layer of said one or more layers isapplied and obtained by using the polymer composition as describedherein.

Also the herein exemplified cable production process may, for example,comprise at least two steps of

a₀) meltmixing said polymer composition, as described herein, optionallytogether with further component(s), and then

a) applying the meltmix obtained from step a₀) on a conductor to form atleast one layer.

The polymer composition, as described herein, may be introduced to stepa₀) of the process, e.g. in pellet form and mixing, i.e. meltmixing, iscarried out in an elevated temperature which melts (or softens) thepolymer material to enable processing thereof.

Further, the layers may, for example, be a) applied by (co)extrusion.The term “(co)extrusion” means herein that in case of two or morelayers, said layers can be extruded in separate steps, or at least twoor all of said layers can be coextruded in a same extrusion step, aswell known in the art.

In one exemplified embodiment the crosslinkable polymer composition maycomprise a crosslinking agent before the polymer composition is used forcable production, whereby the polyethylene and the crosslinking agentcan be blended by any conventional mixing process, e.g. by addition ofthe crosslinking agent to a melt of a composition of polymer, e.g. in anextruder, as well as by adsorption of liquid peroxide, peroxide inliquid form or peroxide dissolved in a solvent on a solid composition ofpolymer, e.g. pellets thereof. Alternatively in this embodiment, thepolyethylene and the crosslinking agent can be blended by anyconventional mixing process. Exemplary mixing procedures include meltmixing, e.g. in an extruder, as well as adsorption of liquid peroxide,peroxide in liquid form or a peroxide dissolved in a solvent of acomposition of the polymer or on pellets thereof. The obtained polymercomposition of components, for example, a.o. the polyethylene and thecrosslinking agent, is then used for an article, e.g. a cable,preparation process.

In another embodiment, the crosslinking agent may be added e.g. in stepa₀) during the preparation of the crosslinkable article, and also formssaid polymer composition of the present invention. When the crosslinkingagent is added during the article preparation process, then, forexample, the crosslinking agent, as described herein, is added in aliquid form at ambient temperature, or is preheated above the meltingpoint thereof or dissolved in a carrier medium, as well known in theart.

Said polymer composition of the present invention may also comprisefurther additive(s), or further additive(s) may be blended to thepolymer composition during a preparation process of an articlecomprising the polymer composition.

Accordingly the process of the invention may, for example, comprise thesteps of

-   -   a₀₀) providing to said step a₀) said polymer composition as        described herein, which comprises        -   at least one polyethylene, and        -   a crosslinking agent,    -   a₀) meltmixing the polymer composition optionally together with        further components, and

a) applying the meltmix obtained from step a₀) on a conductor to form atleast one of said one or more cable layers.

Alternatively, the process of the invention comprises the steps of

-   -   a₀₀) providing to said step a₀) said polymer composition as        described herein, which comprises        -   at least one polyethylene,    -   a_(00′)) adding to said polymer composition at least one        crosslinking agent,    -   a₀) meltmixing the polymer composition and the crosslinking        agent, optionally together with further components, and    -   a) applying the meltmix obtained from step a₀) on a conductor to        form at least one of said one or more cable layers.

In the exemplified process, the a₀) meltmixing of the polymercomposition alone is performed in a mixer or an extruder, or in anycombination thereof, at elevated temperature and, if crosslinking agentis present, then also below the subsequently used crosslinkingtemperature. After a₀) meltmixing, e.g. in said extruder, the resultingmeltmixed layer material is then, for example, a) (co)extruded on aconductor in a manner very well known in the field. Mixers andextruders, such as single or twins screw extruders, which are usedconventionally for cable preparation are suitable for the process of theinvention.

The exemplified embodiment of the process provides the preparation of acrosslinkable cable, e.g. a crosslinkable power cable, wherein theprocess comprises a further step of b) crosslinking the at least onecable layer obtained from step a) comprising the crosslinkablepolyethylene of the polymer composition, wherein the crosslinking isperformed in the presence of a crosslinking agent, e.g. a peroxide.

It is understood and well known that also the other cable layers andmaterials thereof, if present, can be crosslinked at the same time, ifdesired.

Crosslinking can be performed at crosslinking conditions, typically bytreatment at increased temperature, e.g. at a temperature above 140° C.,e.g. above 150° C., such as within the range of 160 to 350° C.,depending on the used crosslinking agent as well known in the field.Typically the crosslinking temperature is at least 20° C. higher thanthe temperature used in meltmixing step a₀) and can be estimated by askilled person.

As a result a crosslinked cable is obtained comprising at least onecrosslinked layer of the polyethylene, or the polymer composition, ofthe invention.

In a further embodiment according to the present invention said polymercomposition is disclosed, wherein the amount of vinyl groups originatesfrom (beside vinyl groups originating from free radical initiatedpolymerisation):

i) polyunsaturated comonomer(s),

ii) chain transfer agent(s),

iii) unsaturated low molecular weight compound(s), e.g. crosslinkingbooster(s) and/or scorch retarder(s), or

iv) any mixture of (i) to (iii).

In general, “vinyl group” means herein CH₂═CH— moiety which can bepresent in any of i) to iv).

The i) polyunsaturated comonomers and ii) chain transfer agents aredescribed herein in relation to the polyethylene of the presentinvention.

The iii) low molecular weight compound(s), if present, may be added intothe polymer composition.

Further, the iii) low molecular weight compound(s) can, for example, becrosslinking booster(s) which may also contribute to the amount of vinylgroups of the polymer composition. The crosslinking booster(s) may bee.g. compound(s) containing at least 2, unsaturated groups, such as analiphatic or aromatic compound, an ester, an ether, or a ketone, whichcontains at least 2, unsaturated group(s), such as a cyanurate, anisocyanurate, a phosphate, an ortho formate, an aliphatic or aromaticether, or an allyl ester of benzene tricarboxylic acid. Examples ofesters, ethers, amines and ketones are compounds selected from generalgroups of diacrylates, triacrylates, tetraacrylates, triallylcyanurate,triallylisocyanurate, 3,9-divinyl-2,4,8,10-tetra-oxaspiro[5,5]-undecane(DVS), triallyl trimellitate (TATM) orN,N,N′,N′,N″,N″-hexaallyl-1,3,5-triazine-2,4,6-triamine (HATATA), or anymixtures thereof. The crosslinking booster can be added in an amount ofsuch crosslinking less than 2.0 wt %, for example, less than 1.5 wt %,e.g. less than 1.0 wt %, for example, less than 0.75 wt %, e.g. lessthan 0.5 wt %, and the lower limit thereof is, for example, at least0.05 wt %, e.g., at least 0.1 wt %, based on the weight of the polymercomposition.

Furthermore, the iii) low molecular weight compound(s) can, for example,be scorch retarder(s) (SR) which may also contribute to the amount ofvinyl groups of the polymer composition.

The scorch retarders (SR) may, e.g., be, as already described herein,unsaturated dimers of aromatic alpha-methyl alkenyl monomers, such as2,4-di-phenyl-4-methyl-1-pentene, substituted or unsubstituteddiphenylethylene, quinone derivatives, hydroquinone derivatives,monofunctional vinyl containing esters and ethers, monocyclichydrocarbons having at least two or more double bonds, or mixturesthereof. For example, the scorch retarder may be selected from2,4-diphenyl-4-methyl-1-pentene, substituted or unsubstituteddiphenylethylene, or mixtures thereof.

The amount of scorch retarder may, for example, be equal to, or morethan, 0.005 wt %, based on the weight of the polymer composition.Further, the amount of scorch retarder may, for example, be equal to, ormore than, 0.01 wt %, equal to, or more than, 0.03 wt %, or equal to, ormore than, 0.04 wt %, based on the weight of the polymer composition.

Further, the amount of scorch retarder may, for example, be equal to, orless than, 2.0 wt %, e.g., equal to, or less than, 1.5 wt %, based onthe weight of the polymer composition. Further, the amount of scorchretarder may, for example, be equal to, or less than, 0.8 wt %, equalto, or less than, 0.75 wt %, equal to, or less than, 0.70 wt %, or equalto, or less than, 0.60 wt %, based on the weight of the polymercomposition. Moreover, the amount of scorch retarder may, for example,be equal to, or less than, 0.55 wt %, equal to, or less than, 0.50 wt %,equal to, or less than, 0.45 wt %, or equal to, or less than, 0.40 wt %,based on the weight of the polymer composition.

Still further, the amount of scorch retarder may, for example, be equalto, or less than, 0.35 wt %, e.g., equal to, or less than, 0.30 wt %,based on the weight of the polymer composition. Further, the amount ofscorch retarder may, for example, be equal to, or less than, 0.25 wt %,equal to, or less than, 0.20 wt %, equal to, or less than, 0.15 wt %, orequal to, or less than, 0.10 wt %, based on the weight of the polymercomposition. Moreover, the amount of scorch retarder may, for example,be equal to, or less than, 0.15 wt %, or equal to, or less than, 0.10 wt%, based on the weight of the polymer composition.

Furthermore, the amount of scorch retarder may, for example, be withinthe range of 0.005 to 2.0 wt %, e.g., within the range of 0.005 to 1.5wt %, based on the weight of the polymer composition. Furtherexemplified ranges are e.g. from 0.01 to 0.8 wt %, 0.03 to 0.75 wt %,0.03 to 0.70 wt %, or 0.04 to 0.60 wt %, based on the weight of thepolymer composition. Moreover, exemplified ranges are e.g. from 0.01 to0.60, to 0.55, to 0.50, to 0.45 or, alternatively, to 0.40 wt %, 0.03 to0. 0.55 or, alternatively, to 0.50 wt %, 0.03 to 0.45 or, alternatively,0.40 wt %, or 0.04 to 0.45 or, alternatively, 0.40 wt %, based on theweight of the polymer composition.

Further, the scorch retarders (SR) may, e.g., also be selected fromgraftable stable organic free radicals, as described in EP1699882 and asalso already described herein.

The polyethylene may, for example, be a copolymer of monomer units withunits of at least one unsaturated comonomer(s) and zero, one, two orthree other comonomer(s), and comprises at least vinyl groups whichoriginate from the polyunsaturated comonomer.

Further, the polyethylene may comprise about 0.05 to about 0.10 vinylgroups per 1000 carbon atoms (C-atoms) which originate from the freeradical initiated polymerisation.

In accordance with the present invention each feature in any of theherein disclosed embodiments, in any category of the present invention,may freely be combined with any feature in any of the other hereindisclosed embodiments.

Determination Methods

Unless otherwise stated in the description or experimental part thefollowing methods were used for the property determinations.

Melt Flow Rate

The melt flow rate (MFR) is determined according to method ISO1133-1:2011 and is indicated in g/10 min. The MFR is an indication ofthe flowability, and hence the processability, of the polymer, here thepolyethylene, or of the polymer composition. The higher the melt flowrate, the lower the viscosity of the polymer, or of the polymercomposition. The MFR is determined at 190° C. for polyethylenes and maybe determined at different loadings such as 2.16 kg (MFR₂) or 21.6 kg(MFR₂₁).

Density

Density is measured on the polymer, i.e. on the polyethylene, accordingto ISO 1183-1 method A:2012. Sample preparation is done by compressionmoulding in accordance with ISO 17855-2:2016.

Methods ASTM D3124-98, and ASTM D6248-98, to Determine Amount of DoubleBonds in the Polymer Composition or in the Polymer, i.e. thePolyethylene

The method ASTM D6248-98 apply for determination of double bonds, both,in the polymer composition and in the polyethylene. Determination ofdouble bonds of the polymer composition is made either on thepolyethylene or, alternatively, on the polymer composition. The polymercomposition and the polyethylene are, hereinafter in this methoddescription, referred to as “the composition” and “the polymer”,respectively.

The methods ASTM D3124-98, and ASTM D6248-98, include on one hand aprocedure for the determination of the amount of double bonds/1000C-atoms which is based upon the ASTM D3124-98 method. In the ASTMD3124-98 method, a detailed description for the determination ofvinylidene groups/1000 C-atoms is given based on2,3-dimethyl-1,3-butadiene. In the ASTM D6248-98 method, detaileddescriptions for the determination of vinyl and trans-vinylenegroups/1000 C-atoms are given based on 1-octene and trans-3-hexene,respectively. The described sample preparation procedure therein hashere been applied for the determination of vinyl groups/1000 C-atoms andtrans-vinylene groups/1000 C-atoms in the present invention. The ASTMD6248-98 method suggests possible inclusion of the bromination procedureof the ASTM D3124-98 method but the samples with regard to the presentinvention were not brominated. We have demonstrated that thedetermination of vinyl groups/1000 C-atoms and trans-vinylenegroups/1000 C-atoms can be done without any significant interferenceseven without subtraction of spectra from brominated samples. For thedetermination of the extinction coefficient for these two types ofdouble bonds, the following two compounds have been used: 1-decene forvinyl and trans-4-decene for trans-vinylene, and the procedure asdescribed in ASTM-D6248-98 was followed with above the mentionedexception.

The total amount of vinyl bonds, vinylidene bonds and trans-vinylenedouble bonds of “the polymer” was analysed by means of IR spectrometryand given as the amount of vinyl bonds, vinylidene bonds andtrans-vinylene bonds per 1000 carbon atoms.

Further, the total amount of vinyl and trans-vinylene double bonds of“the composition”, with a possible contribution of double bonds from anyused unsaturated low molecular weight compound (iii), may also beanalysed by means of IR spectrometry and given as the amount of vinylbonds, vinylidene bonds and trans-vinylene bonds per 1000 carbon atoms.

The composition or polymer to be analysed were pressed to thin filmswith a thickness of 0.5-1.0 mm. The actual thickness was measured. FT-IRanalysis was performed on a Perkin Elmer Spectrum One. Two scans wererecorded with a resolution of 4 cm⁻¹.

A base line was drawn from 980 cm⁻¹ to around 840 cm⁻¹. The peak heightswere determined at around 910 cm⁻¹ for vinyl and around 965 cm⁻¹ fortrans-vinylene. The amount of double bonds/1000 carbon atoms wascalculated using the following formulae:vinyl/1000 C-atoms=(14×Abs)/(13.13×L×D)trans-vinylene/1000 C-atoms=(14×Abs)/(15.14×L×D)

-   -   wherein    -   Abs: absorbance (peak height)    -   L: film thickness in mm    -   D: density of the material (g/cm³)

The molar absorptivity, ε, i.e. 13.13 and, 15.14, respectively, in theabove calculations was determined as l·mol⁻¹·mm⁻¹ via:ε=Abs/(C×L)

where Abs is the maximum absorbance defined as peak height, C theconcentration (mol·l⁻¹) and L the cell thickness (mm).

For polymers with a polar comonomer content>0.4% determination ofunsaturated groups might be disturbed by neighbouring FTIR peaks. Analternative baseline approach may yield a more accurate representationof the unsaturated group content. Overall estimation of small peaksclose to larger peaks could lead to an underestimation. Alternative baseline positions could be 880 and 902 cm⁻¹ for vinyl, 902 and 920 cm⁻¹ forvinylidene, and 954 and 975 cm⁻¹. For higher unsaturated group contentthe base lines for vinyl and vinylidene could be combined.

The methods ASTM D3124-98, and ASTM D6248-98, include on the other handalso a procedure to determine the molar extinction coefficient. At leastthree 0.18 mol·l⁻¹ solutions in carbon disulphide (CS₂) were used andthe mean value of the molar extinction coefficient used.

The amount of vinyl groups originating from the polyunsaturatedcomonomer per 1000 carbon atoms was determined and calculated asfollows:

The polymer to be analysed and a reference polymer have been produced onthe same reactor, basically using the same conditions, i.e. similar peaktemperatures, pressure and production rate, but with the only differencethat the polyunsaturated comonomer is added to the polymer to beanalysed and not added to reference polymer. The total amount of vinylgroups of each polymer was determined by FT-IR measurements, asdescribed herein. Then, it is assumed that the base level of vinylgroups, i.e. the ones formed by the process and from chain transferagents resulting in vinyl groups (if present), is the same for thereference polymer and the polymer to be analysed with the only exceptionthat in the polymer to be analysed also a polyunsaturated comonomer isadded to the reactor. This base level is then subtracted from themeasured amount of vinyl groups in the polymer to be analysed, therebyresulting in the amount of vinyl groups/1000 carbon atoms, which resultfrom the polyunsaturated comonomer.

The Methods ASTM D3124-98, and ASTM D6248-98, Include a CalibrationProcedure for Measuring the Double Bond Content of an Unsaturated LowMolecular Weight Compound (iii), if Present (Referred Below as Compound)

The molar absorptivity for Compound (e.g. a crosslinking booster or ascorch retarder compound as exemplified in the description) can bedetermined with said methods according to ASTM D6248-98. At least threesolutions of the Compound in CS₂ (carbon disulfide) are prepared. Theused concentrations of the solutions are close to 0.18 mol/l. Thesolutions are analysed with FTIR and scanned with resolution 4 cm⁻¹ in aliquid cell with path length 0.1 mm. The maximum intensity of theabsorbance peak that relates to the unsaturated moiety of theCompound(s) (each type of carbon-carbon double bonds present) ismeasured.

The molar absorptivity, ε, in l·mol⁻¹·mm⁻¹ for each solution and type ofdouble bond is calculated using the following equation:ε=(1/CL)×Abs

C=concentration of each type of carbon-carbon double bond to bemeasured, mol/l

L=cell thickness, mm

Abs=maximum absorbance (peak height) of the peak of each type ofcarbon-carbon double bond to be measured, mol/l.

The average of the molar absorptivity, ε, for each type of double bondis calculated. Further, the average molar absorptivity, ε, of each typeof carbon-carbon double bond can then be used for the calculation of theconcentration of double bonds in the reference polymer and the polymersamples to be analysed.

Rheology, Dynamic (Viscosity) Method ISO 6721-1:

Dynamic rheological properties of the polymer, here the polyethylene, orof the polymer composition (also measured on the polyethylene) may bedetermined using a controlled stress rheometer, using a parallel-plategeometry (25 mm diameter) and a gap of 1.8 mm between upper and bottomplates. Previous to test, samples need to be stabilized by dry blendingpellets together with 0.25-0.3% Irganox B225. Irganox B 225 is a blendof 50% Irganox 1010, Pentaerythritoltetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), CAS-no.6683-19-8 and 50% Irgafos 168, Tris(2,4-di-tert-butylphenyl) phosphite,CAS-no. 31570-04-4. Note that to add an antioxidant, here Irganox B225,is normally not the standard procedure of method ISO 6721-1.

A compression moulding process is performed using the followingconditions: The pellets are melted for 2 minutes at 190° C. at anypressure and thereafter with a load of 100 kg/cm² during 2 min. Afterpressing, the material is allowed to cool to room temperature stillunder pressure for 30 minutes. The final thickness of the plaques is 1.8mm.

Frequency sweep test, i.e. the “Rheology, dynamic (Viscosity) method”,was performed according to the ISO standard method, ISO 6721-1 with anangular frequency range from 500 to 0.02 rad/s. All experiments wereconducted under nitrogen atmosphere at a constant temperature of 190° C.and strain within the linear viscoelastic region. During analysis,storage modulus (G′), loss modulus (G″), complex modulus (G*) andcomplex viscosity (η*) were recorded and plotted versus frequency (ω).The measured values of complex viscosity (η*) at angular frequency of0.05, 100 and 300 rad/s are taken from test. The abbreviation of theseparameters are η*_(0.05), η*₁₀₀ and η*₃₀₀ respectively.

The zero viscosity η*₀ value is calculated using Carreau-Yasuda model.For cases when the use of this model for the estimation of the Zeroshear viscosity is not recommendable, a rotational shear test at lowshear rate is performed. This test is limited to a shear rate range of0.001 to 1 s⁻¹ and a temperature of 190° C.

Preparation of Crosslinked Plaque, i.e. the Method for CrosslinkingPlaque:

Preparation of Crosslinked Plaque when Using Dicumyl Peroxide (DCP) ortert-butylcumyl-peroxide (TBCP) as Peroxide, i.e. the Method forCrosslinking Plaque

The crosslinked plaque is prepared from of pellets of the test polymercomposition, i.e. a polymer composition comprising the polyethyleneaccording to the present invention and a polymer composition comprisinga comparative polyethylene, which were compression moulded using thefollowing conditions: First the pellets are melted at 120° C. for 1 minunder a pressure of 61 N/cm². Then the temperature is increased to 180°C. at a rate of 18 K/min and at the same time the pressure is increasedto 614 N/cm². The temperature is maintained at 180° C. for 10 min. Theplaques then become crosslinked by means of the peroxide present in thepolymer composition. The total crosslinking time is 14 minutes whichincludes the time for increasing the temperature from 120 to 180° C.After completed crosslinking the crosslinked plaques, i.e. thecrosslinked polymer composition according to the present invention andthe crosslinked comparative polymer composition, is cooled to roomtemperature with a cooling rate of 15 K/min still under pressure. Thefinal thickness of the plaques is 1.5 mm.

Preparation of Crosslinked Plaque when Using2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, i.e. Trigonox® 145-E85,(T145E85) as Peroxide, i.e. the Method for Crosslinking Plaque

The crosslinked plaque is prepared from of pellets of the test polymercomposition, i.e. the polymer composition according to the presentinvention and the comparative polymer composition, which werecompression moulded using the following conditions: First the pelletsare melted at 120° C. for 1 min under a pressure of 61 N/cm². Then thetemperature is increased to 180° C. at a rate of 18 K/min and at thesame time the pressure is increased to 614 N/cm². The temperature ismaintained at 180° C. for 20 min. The plaques then become crosslinked bymeans of the peroxide present in the polymer composition. The totalcrosslinking time is 24 minutes which includes the time for increasingthe temperature from 120 to 180° C. After completed crosslinking thecrosslinked plaques, i.e. the crosslinked polymer composition accordingto the present invention and the crosslinked comparative polymercomposition, is cooled to room temperature with a cooling rate of 15K/min still under pressure. The final thickness of the plaques is 1.5mm.

Gas Chromatography (GC)-Analysis Protocol, i.e. Method for GC-Analysis

GC-Analysis Protocol (Plaque), i.e. Method for GC-Analysis

The volatile peroxide decomposition products, herein methane (CH₄),content is given in ppm (weight) and is determined by gas chromatography(GC) from a crosslinked sample of the polymer composition according tothe present invention and of the comparative polymer composition. Saidcrosslinking has been performed as described in the method forcrosslinking plaque.

A sample specimen with a thickness of 1.5 mm and with a weight of 1 g iscut from the middle of the crosslinked plaque, i.e. the crosslinkedpolymer composition according to the present invention and thecrosslinked comparative polymer composition, directly after thecrosslinking step is complete. The obtained sample is placed in a 120 mlhead space bottle with an aluminium crimp cup with teflon seal and heattreated at 60° C. for 1.5 h to equilibrate any gaseous volatiles presentin said sample. Then 0.2 ml of the gas captured in the sample bottle isinjected into the gas chromatograph, wherein the presence and content ofthe volatiles, e.g. methane, which are desired to be measured isanalysed. Double samples are analysed and the reported methane contentvalue is an average of both analyses. The instrument used herein was anAgilent GC 7890A with an Al₂O₃/Na₂SO₄— column with the dimensions 0.53mm×50 m and a film thickness of 10 μm, supplied by Plot Ultimetal.Helium was used as carrier gas and FID detection was used.

Method for Hot Set Determination

Hot Set Method for Sample from Crosslinked Plaques

The hot set elongation, as well as the permanent deformation weredetermined on samples taken from crosslinked plaques, i.e. a crosslinkedpolymer composition comprising the polyethylene according to the presentinvention and of crosslinked polymer composition comprising acomparative polyethylene. These properties were determined according toIEC 60811-507:2012. In the hot set test, a dumbbell of the testedmaterial is equipped with a weight corresponding to 20 N/cm². First ofall the specimen is marked with reference lines. From the middle of thespecimen, two reference lines (one on each side) are made. The distancebetween the two lines, L0 is 20 mm. This specimen is put into an oven at200° C. with the weight correponding to 20 N/cm² and after 15 minutes,the hot set elongation is measured as follow. The distance betweenreference lines after 15 min at 200° C. is called L1 and is measured.Then the elongation after 15 min is calculated as follows: hot setelongation (%)=((L1*100)/L0)−100. Subsequently, the weight is removedand the sample is allowed to relax for 5 minutes at 200° C. Then, thesample is taken out from the oven and is cooled down to roomtemperature. After cooling, the distance L2 between the 2 referencelines is measured and the permanent deformation is calculated as follow:permanent deformation (%)=(L2*100)/L0)−100.

The crosslinked plaques were prepared as described under Preparation ofcrosslinked plaque, i.e. the method for crosslinking plaque, and thedumbbells specimens are prepared from a 1.5 mm thick crosslinked plaqueaccording to ISO 527-2/5A:2012.

Experimental Part

EXAMPLES

The polyethylenes are all low density polyethylenes polymerised in ahigh pressure tubular reactor.

Inventive Example 1

Polymer 1, i.e. polyethylene in accordance with the present invention,i.e. poly (ethylene-co-1,7-octadiene) polymer with 0.71 vinylgroups/1000 carbon atoms (C), Density=922.3 kg/m³, MFR₂=0.68 g/10 min)

Ethylene with recycled CTA was compressed in a 5-stage precompressor anda 2-stage hyper compressor with intermediate cooling to reach initialreaction pressure of ca 2900 bar. The total compressor throughput was ca30 tons/hour. In the compressor area approximately 1.2 kg/hour ofpropion aldehyde (PA, CAS number: 123-38-6) was added together withapproximately 87 kg propylene/hour as chain transfer agents to maintainan MFR₂ of 0.68 g/10 min. Here also 1,7-octadiene was added to thereactor in amount of 56 kg/h. The compressed mixture was heated to 164°C. in a preheating section of a front feed three-zone tubular reactorwith an inner diameter of ca 40 mm and a total length of 1200 meters. Amixture of commercially available peroxide radical initiators dissolvedin isododecane was injected just after the preheater in an amountsufficient for the exothermal polymerisation reaction to reach peaktemperatures of ca 277° C. after which it was cooled to approximately206° C. The subsequent 2^(nd) and 3^(rd) peak reaction temperatures were270° C. and 249° C. respectively with a cooling in between to 217° C.The reaction mixture was depressurised by a kick valve, cooled and theresulting polymer 1 was separated from unreacted gas.

Inventive Example 2 Polymer 2, i.e. polyethylene in accordance with thepresent invention, i.e. poly (ethylene-co-1,7-octadiene) polymer with1.33 vinyl groups/1000 C, Density=924.3 kg/m³, MFR₂=0.94 g/10 min)

Ethylene with recycled CTA was compressed in a 5-stage precompressor anda 2-stage hyper compressor with intermediate cooling to reach initialreaction pressure of ca 2800 bar. The total compressor throughput was ca30 tons/hour. In the compressor area approximately 2.3 kg/hour ofpropion aldehyde (PA, CAS number: 123-38-6) was added as chain transferagent to maintain an MFR₂ of 0.94 g/10 min. Here also 1,7-octadiene wasadded to the reactor in amount of 144 kg/h. The compressed mixture washeated to 160° C. in a preheating section of a front feed three-zonetubular reactor with an inner diameter of ca 40 mm and a total length of1200 meters. A mixture of commercially available peroxide radicalinitiators dissolved in isododecane was injected just after thepreheater in an amount sufficient for the exothermal polymerisationreaction to reach peak temperatures of ca 274° C. after which it wascooled to approximately 207° C. The subsequent 2^(nd) and 3^(rd) peakreaction temperatures were 257° C. and 227° C. respectively with acooling in between to 211° C. The reaction mixture was depressurised bya kick valve, cooled and the resulting polymer 2 was separated fromunreacted gas.

Inventive Example 3

Polymer 3, i.e. polyethylene in accordance with the present invention,i.e. poly (ethylene-co-1,7-octadiene) polymer with 1.34 vinylgroups/1000 C, Density=924.9 kg/m³, MFR₂=1.46 g/10 min)

Ethylene with recycled CTA was compressed in a 5-stage precompressor anda 2-stage hyper compressor with intermediate cooling to reach initialreaction pressure of ca 2800 bar. The total compressor throughput was ca30 tons/hour. In the compressor area approximately 3.9 kg/hour ofpropion aldehyde (PA, CAS number: 123-38-6) was added as chain transferagent to maintain an MFR₂ of 1.46 g/10 min. Here also 1,7-octadiene wasadded to the reactor in amount of 148 kg/h. The compressed mixture washeated to 159° C. in a preheating section of a front feed three-zonetubular reactor with an inner diameter of ca 40 mm and a total length of1200 meters. A mixture of commercially available peroxide radicalinitiators dissolved in isododecane was injected just after thepreheater in an amount sufficient for the exothermal polymerisationreaction to reach peak temperatures of ca 273° C. after which it wascooled to approximately 207° C. The subsequent 2^(nd) and 3^(rd) peakreaction temperatures were 257° C. and 226° C. respectively with acooling in between to 209° C. The reaction mixture was depressurised bya kick valve, cooled and the resulting polymer 3 was separated fromunreacted gas.

Comparative Example 1

Comparative polymer 1, i.e. polyethylene with 0.27 vinyl groups/1000 C,Density=not measured, MFR₂=0.76 g/10 min)

Ethylene with recycled CTA was compressed in a 5-stage precompressor anda 2-stage hyper compressor with intermediate cooling to reach initialreaction pressure of ca 2800 bar. The total compressor throughput was ca30 tons/hour. In the compressor area approximately 4.1 kg/hour ofpropion aldehyde (PA, CAS number: 123-38-6) was added together withapproximately 80 kg propylene/hour as chain transfer agents to maintainan MFR₂ of 0.76 g/10 min. The compressed mixture was heated to 163° C.in a preheating section of a front feed three-zone tubular reactor withan inner diameter of ca 40 mm and a total length of 1200 meters. Amixture of commercially available peroxide radical initiators dissolvedin isododecane was injected just after the preheater in an amountsufficient for the exothermal polymerisation reaction to reach peaktemperatures of ca 284° C. after which it was cooled to approximately224° C. The subsequent 2^(nd) and 3^(rd) peak reaction temperatures were283° C. and 270° C. respectively with a cooling in between to 233° C.The reaction mixture was depressurised by a kick valve, cooled andpolymer was separated from unreacted gas.

Comparative Example 2

Comparative polymer 2, i.e. polyethylene with 0.29 vinyl groups/1000 C,Density=not measured, MFR₂=0.78 g/10 min)

Ethylene with recycled CTA was compressed in a 5-stage precompressor anda 2-stage hyper compressor with intermediate cooling to reach initialreaction pressure of ca 2600 bar. The total compressor throughput was ca30 tons/hour. In the compressor area approximately 3.6 kg/hour ofpropion aldehyde (PA, CAS number: 123-38-6) was added together withapproximately 91 kg propylene/hour as chain transfer agents to maintainan MFR₂ of 0.78 g/10 min. The compressed mixture was heated to 166° C.in a preheating section of a front feed three-zone tubular reactor withan inner diameter of ca 40 mm and a total length of 1200 meters. Amixture of commercially available peroxide radical initiators dissolvedin isododecane was injected just after the preheater in an amountsufficient for the exothermal polymerisation reaction to reach peaktemperatures of ca 279° C. after which it was cooled to approximately227° C. The subsequent 2^(nd) and 3^(rd) peak reaction temperatures were273° C. and 265° C. respectively with a cooling in between to 229° C.The reaction mixture was depressurised by a kick valve, cooled andpolymer was separated from unreacted gas.

Comparative Example 3

Comparative polymer 4, i.e. polyethylene with 0.37 vinyl groups/1000 C,Density=not measured kg/m³, MFR₂=2.07 g/10 min)

Ethylene with recycled CTA was compressed in a 5-stage precompressor anda 2-stage hyper compressor with intermediate cooling to reach initialreaction pressure of ca 2600 bar. The total compressor throughput was ca30 tons/hour. In the compressor area approximately 4 kg/hour of propionaldehyde (PA, CAS number: 123-38-6) was added together withapproximately 119 kg propylene/hour as chain transfer agents to maintainan MFR₂ of 2.07 g/10 min. The compressed mixture was heated to 166° C.in a preheating section of a front feed three-zone tubular reactor withan inner diameter of ca 40 mm and a total length of 1200 meters. Amixture of commercially available peroxide radical initiators dissolvedin isododecane was injected just after the preheater in an amountsufficient for the exothermal polymerisation reaction to reach peaktemperatures of ca 276° C. after which it was cooled to approximately221° C. The subsequent 2^(nd) and 3^(rd) peak reaction temperatures were271° C. and 261° C. respectively with a cooling in between to 225° C.The reaction mixture was depressurised by a kick valve, cooled andpolymer was separated from unreacted gas.

Comparative Example 4

Comparative polymer 5, i.e. poly (ethylene-co-1,7-octadiene) polymerwith 0.77 vinyl groups/1000 C, Density=922.1 kg/m³, MFR₂=1.82 g/10 min)

Ethylene with recycled CTA was compressed in a 5-stage precompressor anda 2-stage hyper compressor with intermediate cooling to reach initialreaction pressure of ca 2900 bar. The total compressor throughput was ca30 tons/hour. In the compressor area approximately 0.8 kg/hour ofpropion aldehyde (PA, CAS number: 123-38-6) was added together withapproximately 123 kg propylene/hour as chain transfer agents to maintainan MFR₂ of 1.82 g/10 min. Here also 1,7-octadiene was added to thereactor in amount of 55 kg/h. The compressed mixture was heated to 163°C. in a preheating section of a front feed three-zone tubular reactorwith an inner diameter of ca 40 mm and a total length of 1200 meters. Amixture of commercially available peroxide radical initiators dissolvedin isododecane was injected just after the preheater in an amountsufficient for the exothermal polymerisation reaction to reach peaktemperatures of ca 274° C. after which it was cooled to approximately204° C. The subsequent 2^(nd) and 3^(rd) peak reaction temperatures were261° C. and 244° C. respectively with a cooling in between to 216° C.The reaction mixture was depressurised by a kick valve, cooled andpolymer was separated from unreacted gas.

Characterisation data in Table 1 and Table 2

TABLE 1 MFR₂ (g/10 η* ₀ η* _(0.05) η* ₃₀₀ Polymer min) (Pa s) (Pa s) (Pas) Inventive Polymer 1 0.68 47270 22290 337 Example 1 Inventive Polymer2 0.94 39200 18715 316 Example 2 Inventive Polymer 3 1.46 20670 12675288 example 3 Comparative Comparative 0.76 Not Not Not example 1 polymer1 measured measured measured Comparative Comparative 0.78 30860 20140378 example 2 polymer 2 Comparative Comparative 2.07 8767 7614.5 300example 3 polymer 4 Comparative Comparative 1.82 11275 8814 277 example4 polymer 5

TABLE 2 Vinyl/ Vinylidene/ Trans-vinylene/ Material 1000 C 1000 C 1000 CInventive 0.71 0.17 0.08 Example 1 Inventive 1.33 0.17 0.14 Example 2Inventive 1.34 0.17 0.14 example 3 Comparative 0.27 0.18 0.04 example 1Comparative 0.29 0.17 0.04 example 2 Comparative 0.37 0.17 0.04 example3 Comparative 0.77 0.17 0.08 example 4

The Polymer Composition

Formulations, i.e. the polymer composition, using the polyethylene, ofthe present invention, as described herein, and crosslinking agent, andalso comparative examples, have been prepared on lab scale and compared.The crosslinking agent was added to the polyethylene by distributing thecrosslinking agent (crosslinking agent is in a liquid form) at 70° C.onto the polyethylene pellets. The wet pellets were kept at 80° C. untilthe pellets became dry. The amount of crosslinking agent, e.g. peroxide,for example, DCP, was the same for all examples to show the crosslinkingresponse as measured by the method for Hot Set Determination (with aload of 20 N/cm²). The hot set elongation, as well as the permanentdeformation, were determined, see table 3, as described in determinationmethod under “Hot Set method for sample from a crosslinked plaque”, on1.5 mm thick plaques. The 1.5 mm thick plaques were compression mouldedand crosslinked at 180° C. as described in the determination methodunder “preparation of crosslinked plaques, i.e. method for crosslinkingplaques”.

TABLE 3 Inventive Polymer Composition Example (Inv.P.C.Ex.) 1 andInv.P.C.Ex.2, and Comparative Polymer Composition Examples(Comp.P.C.Ex.) 1-3, Hot set elongation (%) and Permanent deformation.Hot set Permanent elongation (%), deformation Composition 20 N/cm² (%),20 N/cm² Inv.P . C .Ex.1:   72%   2.6% Polymer 1 + 0.55 wt % DCPInv.P.C.Ex.2: 24.2% −2.2% Polymer 2 + 0.55 wt % DCP Comp.P.C.Ex.1: Allsamples All samples Comparative Polymer 2 + broke broke 0.55 wt % DCPComp.P.C.Ex.2: All samples All samples Comparative Polymer 4 + brokebroke 0.55 wt % DCP Comp.P.C.Ex.3: All samples All samples ComparativePolymer 5 + broke broke 0.55 wt % DCP DCP = dicumylperoxide (CAS number80-43-3)

The polyethylene according to the present invention, as represented bythe Inventive Examples 1-3 (see tables 1 and 2) and the InventivePolymer Composition Examples 1-2 (see table 3), has, in comparison withother polyethylenes having a similar viscosity under processingconditions illustrated by complex viscosity (η*) at 300 rad/sec, asrepresented by the Comparative Examples 3-4 (see tables 1 and 2) and theComparative Polymer Composition Example 2-3 (see table 3), been shown tohave both

an improved sagging resistance illustrated by the complex viscosity (η*)at 0.05 rad/sec (see Table 1), as well as,

an improved crosslinking degree illustrated by “Hot set elongation” (seeTable 3).

Moreover, the polyethylene according to the present invention, asrepresented by the Inventive Examples 1-3 (see tables 1 and 2) and theInventive Polymer Composition Examples 1-2 (see table 3), has, incomparison with even other polyethylenes instead having a similarsagging resistance, again illustrated by the complex viscosity (η*) at0.05 rad/sec (see Table 1), as represented by the Comparative Example 2(see tables 1 and 2) and Comparative Polymer Composition Example 1 (seetable 3), also shown

an improved viscosity under processing conditions illustrated by complexviscosity (η*) at 300 rad/sec, as well as,

an improved crosslinking degree illustrated by “Hot set elongation” (seeTable 3).

Thus, the polyethylene according to the present invention, as definedherein, surprisingly combines in one polymer, i.e. in the polyethyleneaccording to the present invention:

good processability (e.g. a good flowability), i.e. viscosity underprocessing conditions here illustrated by complex viscosity (η*) at 300rad/sec, which is generally only associated with polymers having acomparably higher MFR₂, with excellent sagging resistance, hereillustrated by the complex viscosity (η*) at 0.05 rad/sec, generallyonly associated with polymers having a comparably lower MFR₂.

Moreover, the polyethylene, according to the present invention, hassurprisingly also been shown to have an improved crosslinking degree asillustrated by “Hot set elongation”.

The invention claimed is:
 1. A polyethylene, characterized in that: thepolyethylene has a melt flow rate at 2.16 kg loading (MFR₂), determinedaccording to method ISO 1133-1:2011, wherein the MFR₂is A g/10 min and0.5≤A≤1.70; and the polyethylene contains a total amount of vinylgroups, determined according to method ASTM D6248-98, which is B vinylgroups per 1000 carbon atoms and 0.45≤B.
 2. The polyethylene accordingto claim 1, wherein 0.58≤B.
 3. The polyethylene according to claim 1,wherein 0.5≤A≤1.65, 1.60, 1.55 or 1.50.
 4. The polyethylene according toclaim 1, wherein B≤3.0.
 5. The polyethylene according to claim 1,wherein the polyethylene is an unsaturated LDPE polymer.
 6. Thepolyethylene according to claim 1, wherein the polyethylene is ahomopolymer of ethylene or is an unsaturated copolymer comprising one ormore polyunsaturated comonomer(s).
 7. The polyethylene according toclaim 1, wherein the polyethylene is a copolymer of: a monomer; at leastone polyunsaturated comonomer; and zero or one or more othercomonomer(s); wherein said total amount of vinyl groups (B) present inthe polyethylene includes vinyl groups originating from said at leastone polyunsaturated comonomer.
 8. The polyethylene according to claim 1,wherein the polyethylene is a copolymer of: a monomer; and at least onepolyunsaturated comonomer; wherein the polyunsaturated comonomer is astraight carbon chain with at least 8 carbon atoms, at least twonon-conjugated double bonds of which at least one is terminal, and atleast 4 carbon atoms between the non-conjugated double bonds.
 9. Thepolyethylene according to claim 1, wherein the polyethylene is acopolymer of ethylene and 1,7-octadiene.
 10. The polyethylene accordingto claim 1, wherein the polyethylene is an unsaturated low densitypolyethylene (LDPE) homopolymer or copolymer.
 11. The polyethyleneaccording to claim 1, wherein 0.88≤B.
 12. The polyethylene according toclaim 1, wherein B≥0.95, 1.00, 1.05 or 1.10.
 13. The polyethyleneaccording to claim 1, wherein the polyethylene has a complex viscosity(η*) at 0.05 rad/sec, which is X Pas, and 10000≤X≤30000, wherein thecomplex viscosity (η*) is determined according to method ISO 6721-1 onstabilized samples of the polyethylene.
 14. The polyethylene accordingto claim 1, wherein the polyethylene has: a complex viscosity (η*) at0.05 rad/sec, which is X Pas, and 12000≤X≤28000, and a complex viscosity(η*) at 300 rad/sec, which is Y Pas, and 250≤Y≤330, wherein the complexviscosities (η*) are determined according to method ISO 6721-1 onstabilized samples of the polyethylene.
 15. The polyethylene accordingto claim 1, wherein the polyethylene has: a complex viscosity (η*) at0.05 rad/sec, which is X Pas, and 15500≤X≤24000, and a complex viscosity(η*) at 300 rad/sec, which is Y Pas, and 250≤Y≤330, wherein the complexviscosities (η*) are determined according to method ISO 6721-1 onstabilized samples of the polyethylene.
 16. A polymer composition, whichis crosslinkable or crosslinked, wherein the polymer compositioncomprises, or is obtained from, the polyethylene according to claim 1.17. An article comprising the polyethylene according to claim 1 whereinthe article is a cable or a cable layer.
 18. The article according toclaim 17, wherein the article is a power cable or a power cable layer.19. The article according to claim 17, wherein the article comprises aninsulating layer.
 20. A process for producing the polyethylene accordingto claim 1, wherein the process is a continuous and high pressureprocess.
 21. A process for producing the article according to claim 17,wherein the process comprises using the polyethylene to produce thearticle.
 22. The process according to claim 21, wherein said article isa power cable and wherein said process comprises the steps of: a₀)meltmixing the polyethylene, optionally together with furthercomponents; and a) applying the meltmix obtained from step a₀) on aconductor to form at least one cable layer.
 23. The process according toclaim 22, wherein said article is a crosslinked power cable and whereinsaid process further comprises the step of: b) crosslinking the at leastone cable layer obtained from step a).
 24. The polyethylene according toclaim 8, wherein the polyunsaturated comonomer is selected from thegroup consisting of 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene,1,13-tetradecadiene, and mixtures thereof.